Deshaun Watson came off the bench and gave the Texans a bit of a spark on Sunday. (Tim Warner/Getty Images)

First and 10: September 12

First: Houston should turn to Deshaun Watson

1. Eagles may be Cowboys’ top threat | 2. Replay gets Redskins review right
3. Ravens defense potent once more | 4. Rams loving early returns on new coaches | 5. Colts, and Pagano, are in trouble
6. The “other” Watt7. First place Bills? Naturally. | 8. Good day for new coaches
9. The biggest QB takeaways from Week 110. Time to believe in the Jags?

FIRST …

If you’re willing to bench your starting quarterback one half into your first game, it means you picked the wrong guy to begin with, and you know it.

That’s where the Houston Texans are right now.

The Texans entered the season with Tom Savage as their starter, seemingly on the premise that he is a reasonably proficient game-manager able to avoid costly mistakes and allow Houston’s defense to do the heavy lifting and churn out workmanlike victories.

Never mind that the Texans, after being denied a chance to sign Tony Romo in the offseason when he opted for retirement and the CBS broadcast booth, traded up to select Deshaun Watson 12th overall in the NFL draft. Forget that Watson had his eye-catching moments during training camp and the preseason and brings an improvisational ability to the offense that Savage does not possess. The Texans went with the seemingly safer choice, giving the starting nod to the more experienced player.

That lasted one half Sunday, at which point Coach Bill O’Brien sat down Savage and went to Watson. The Texans trailed the Jacksonville Jaguars, 19-0, and Savage had been sacked six times while completing seven of 13 passes for 62 yards.

Things improved only slightly for the Texans with Watson on the field. He threw a touchdown pass. But he also threw an interception and was sacked four times in a 12-for-23, 102-yard passing performance. He also ran for 16 yards on two carries in the Texans’ 29-7 loss.

The Texans play again Thursday night at Cincinnati, and O’Brien was not ready to say Sunday which quarterback will start against the Bengals.

“We’ve got a quick turnaround here so we’ve got a lot of film to watch, a lot of things to get caught up on,” O’Brien said during his postgame news conference. “The decision to go with Deshaun really didn’t have a whole lot to do with — it had more to do with could we find a spark, could we find somebody that could maybe make a play, that could escape the pocket, things like that. I thought that Tom really hung in there and played very tough. But we had a hard time protecting him and so I just made the decision to go with Deshaun.”

It’s clear that the Texans should turn to Watson. He is the future, and has the potential to develop into a franchise quarterback. He has the ability to escape pass rushers and compensate for the shortcomings of an offensive line that remains without holdout left tackle Duane Brown and was overwhelmed Sunday by the Jaguars.

The even bigger issue might be a defense that allowed Jaguars tailback Leonard Fournette to run for 100 yards Sunday in his first regular season game (maybe the NFL is easy, after all) and failed to force Jacksonville’s beleaguered quarterback, Blake Bortles, into either a sack or an interception. The Texans led the league in total defense last season even with J.J. Watt hurt. Now Watt is back, and the defense is supposed to be even better. That wasn’t the case Sunday.

“It was a terrible day on offense,” O’Brien said. “But it wasn’t that much better defensively. Like I said, we’ll have to watch the film. We’ve got to watch the tape. But there were just some things out there that weren’t good. We have a lot of work to do. We’ve got a quick turnaround here. I told the team we’ve got to stick together. We’ve got to get back to work right away tomorrow.”

… AND TEN

1. Cowboys and Eagles … It’s no surprise the Dallas Cowboys got their season off to a winning start Sunday night at home against the New York Giants. The Cowboys are the front-runner in the NFC East and perhaps in the entire NFC with tailback Ezekiel Elliott in the lineup.

That became possible when U.S. District Judge Amos L. Mazzant III on Friday granted the NFL Players Association’s request for an injunction to keep Elliott’s six-game suspension on hold while Elliott’s legal challenge to the penalty plays out.

It is not clear how much longer Elliott will remain eligible to play. The entire season is possible. But the NFL is said to be contemplating appealing Mazzant’s injunction ruling to the U.S. Court of Appeals for the Fifth Circuit.

What was somewhat surprising about Sunday’s games is the possibility that the Philadelphia Eagles, not the Giants, could emerge as the top challenger to the Cowboys in the NFC East.

The Giants struggled mightily on offense against the Cowboys with wide receiver Odell Beckham Jr. sidelined by the ankle injury he suffered during the preseason. It was a too-familiar refrain from last season, when the Giants were greatly improved on defense but the offense ultimately failed to do its part. That was enough for the Giants to be a playoff team but not to make a run deep into the postseason. If they don’t have Beckham at his dazzling best, the offense again could be what undermines them.

The Eagles, meanwhile, gave a tantalizingly solid performance in beating the Washington Redskins, 30-17, at FedEx Field. Second-year quarterback Carson Wentz, taken second overall in last year’s NFL draft, made some galling mistakes but also some brilliant plays. The defense forced four turnovers. And the Eagles didn’t even fully utilize their big-name newcomers on offense, tailback LeGarrette Blount and wide receivers Alshon Jeffery and Torrey Smith.

The Eagles were a relatively competent team last season when right tackle Lane Johnson was on the field rather than suspended. And if Wentz makes a jump in Year 2, they perhaps could approach or even reach contender status this season. Sunday’s win made for a good day for the team’s second-year coach, Doug Pederson, who’d faced some criticism recently and was rewarded by his players with a postgame Gatorade dousing on the sideline.

“It’s everything that I’ve been telling you guys,” Pederson said after the game. “Just ask the players how they feel about me. Just give this all to the players in that locker room. They battled. They hung in there through adversity and we pulled it out.”

2. Replay ruling on Cousins’s fumble … Many were highly critical of the instant replay ruling that sealed the Redskins’ loss to the Eagles. Redskins quarterback Kirk Cousins lost a fumble on a sack, and the Eagles recovered the loose football and scored a clinching touchdown with about a minute and a half to play. The Redskins offense remained on the field during the replay review, convinced that the fumble call would be overturned and the play instead would be ruled an incomplete pass.

However, one angle seemed to show the football slipping from Cousins’s hand before he moved his arm forward in the passing motion. If that is indeed what happened, it is a fumble and not an incompletion. There was, at the very least, not enough evidence to overturn the original call of a fumble, given what that replay angle appeared to show.

“There was nothing conclusive that would overturn the ruling on the field,” referee Brad Allen told The Post’s Master Tesfatsion, who served as the pool reporter. “All the views we had were inconclusive, so we had to stay with the ruling on the field.”

Remember that the NFL has centralized its replay review system this year, meaning that rulings are made by members of the league’s officiating department in New York in consultation with the referee on the field. This was a significant test of that system on the season’s first Sunday.

“I’m just glad it was in our favor,” Pederson said.

3. Ravens’ defense … In training camp, the Baltimore Ravens were excited about their defense. Standing on the field at the Naval Academy in Annapolis after a training camp practice there, veteran defensive back Lardarius Webb expressed his optimism about the unit’s infusion of youth among its pass rushers to go with a fortified and experienced secondary.

“There’s a lot of young rushers who are just gonna rush, rush, rush, rush, rush,” Webb said that evening. “And then you’ve got Terrell Suggs teaching those guys. It’s gonna be a big year. We’ve got C.J. Mosley, our middle linebacker. He’s growing each year. Our Pro Bowler, our leader. With him getting older and more mature and knowing the game a little bit more, it’s making it easier for our defense. Our defense has no choice but to get better with Tony Jefferson we brought in and Eric Weddle. We’re just looking to be better than we were last year, but kind of continue that strong play I thought we did at the safety position. And to bring in another top, talented safety is gonna be awesome.”

Webb’s enthusiasm was justified, if Opening Day was any indication. The Ravens had five sacks and four interceptions against Bengals quarterback Andy Dalton and shut out Cincinnati, 20-0.

For the Ravens, so much of training camp was about quarterback Joe Flacco’s ailing back, the consternation over whether to sign Colin Kaepernick, and a series of injuries. But the narrative became more positive for the Ravens on Sunday because of the play of their defense. It was a good sign as the team tries to get back into the playoffs after a two-season absence.

4. McVay, Phillips and the Rams … It seemed like a good idea in the offseason when the Los Angeles Rams paired Sean McVay, the youngest head coach in modern NFL history, with the most seasoned and successful of defensive coordinators, Wade Phillips. McVay is an offensive-minded coach tasked with making a franchise quarterback out of Jared Goff, the top overall choice in last year’s NFL draft. Phillips was brought in to do what he does — make the defense immediately and significantly better — and hopefully buy some time for McVay and Goff to experience their expected growing pains.

So far, so good … and then some.

Phillips’s defense was terrific Sunday against Indianapolis, with two touchdowns on interception returns and a safety. And that was without dominant defensive tackle Aaron Donald, who ended his holdout late last week, but didn’t play.

Goff, too, looked like a new player, throwing for 306 yards and a touchdown in a 21-for-29 passing display. He was sacked only once and did not throw an interception.

One game into their Rams tenure, McVay and Phillips resemble miracle workers. Now all they have to do is keep that going. Not much to ask, huh?

5. Woeful Colts … The Colts were on the wrong end of that 46-9 decision to the Rams, and it could be a long, demoralizing season in Indianapolis. Quarterback Andrew Luck has not returned from shoulder surgery and his replacement, Scott Tolzien, clearly is not the answer. He was sacked four times and had a pair of pick-sixes before being replaced by Jacoby Brissett, the second-year quarterback just obtained in a roster-cutdown trade with the New England Patriots. Some observers consider this a win-or-else season for Colts Coach Chuck Pagano. It’s not off to a promising beginning.

6. Watt the younger … The Pittsburgh Steelers have an impact player on defense in rookie linebacker T.J. Watt, who had two sacks and an interception in his NFL debut at Cleveland. The younger Watt became the first player to accomplish that since a pair of replacement players in 1987. No one should expect Watt to play at the superstar level of his older brother. But with his intensity and nonstop hustle, he could be a defensive difference-maker on a team capable of again being among the AFC’s top contenders.

7. First-place Bills … The Buffalo Bills are in sole possession of first place in the AFC East. Who thought it would go any other way?

That’s likely to be a temporary situation, of course. The Bills beat the New York Jets in a season opener to avoid in Buffalo, three days after the Patriots lost their opener to the Kansas City Chiefs. The Miami Dolphins didn’t play because their opener against the Tampa Bay Buccaneers was postponed due to Hurricane Irma.

So the Bills should enjoy it for now. Anyone who thinks the Patriots won’t get their issues worked out hasn’t spent much time watching Coach Bill Belichick and quarterback Tom Brady.

8. Rookie coaches … The victories by McVay, Buffalo’s Sean McDermott and Jacksonville’s Doug Marrone made for a 3-1 day for the new head coaches. San Francisco’s Kyle Shanahan suffered the lone defeat in a home loss to the Carolina Panthers. The Los Angeles Chargers’ Anthony Lynn and Denver’s Vance Joseph face off Monday night.

9. QB watch … Quick thoughts on some notable quarterback situations around the league:

* The Panthers’ Cam Newton threw for 171 yards and two touchdowns against the Niners after receiving very limited playing time during the preseason while working his way back from shoulder surgery. It wasn’t the MVP-level Newton of the 2015 season. But it was plenty good enough to beat the 49ers and it was encouraging for the Panthers.

*Flacco wasn’t great against the Bengals, throwing for 121 yards with nine completions. He had a touchdown and an interception, but he didn’t need to be great, given how his defense played. The fact that he was in the lineup was enough. The alternative, remember, is Ryan Mallett.

* Mike Glennon was okay for the Chicago Bears in their loss to the Atlanta Falcons, throwing for 213 yards and a touchdown while going interception-free. But every Bears defeat seemingly puts them that much closer to playing rookie Mitchell Trubisky.

* Josh McCown threw two interceptions in the Jets’ loss to the Bills. The Jets move that much closer to using the No. 1 overall pick in next year’s NFL draft on a quarterback.

* Matthew Stafford’s first regular season pass as the NFL’s highest-paid quarterback was intercepted and returned for a touchdown. No matter. He ended up throwing for four touchdowns as the Detroit Lions came back to beat the Arizona Cardinals.

* The Bengals opted against trading AJ McCarron in the offseason. How long will Dalton be permitted to continue to struggle before Coach Marvin Lewis gives McCarron a chance to take over?

* Browns rookie DeShone Kizer was decent in his NFL debut, throwing for 222 yards and a touchdown. But he didn’t have any answers for Watt. And the Browns are, after all, still the Browns.

10. Believe in the Jags? … The Jaguars have been a fool’s gold team in the NFL in recent years, annually failing to live up to the promise of their young talent. And Sunday’s triumph over the Texans was tempered by the loss of wide receiver Allen Robinson to a left ACL injury, reportedly ending his season.

But this feels like it could actually be time to start believing in the Jaguars. Fournette is the real deal. The pass rush Sunday was impressive, even with the Texans’ issues. Marrone is a good coach who previously did pretty well in Buffalo, considering the circumstances. The addition of Tom Coughlin to the front office provides stability, even if the two-time Super Bowl-winning coach of the Giants refused to say publicly why he wasn’t interested in signing Kaepernick.

So much revolves around Bortles. When he avoids repeated and damaging mistakes, as he managed to do Sunday, the Jaguars are functional. Now he must show that he can do that on a reasonably consistent basis.

More NFL coverage:

Cowboys’ Cole Beasley makes an early bid for NFL’s catch of the year

NFL Week 1: Odell Beckham Jr. inactive, David Johnson injures wrist, anthem protests continue

For bad season openers, there’s the Redskins and Browns, and then everyone else

Eagles QB Carson Wentz makes spectacular plays, big mistakes to begin Year 2

After loss to Packers, the gap between the Seahawks’ defense and offense gets bigger