Wentz eludes linebacker Zach Brown to complete a third and 10 pass last Sunday. (Jonathan Newton/The Washington Post)

After Carson Wentz spun away from two would-be sacks like a 6-foot-5 ballerina to deliver a 58-yard touchdown pass on third and 12, the Washington Redskins only could applaud the Houdini-like elusiveness of Philadelphia’s second-year quarterback.

Had it been a lone, freakishly athletic play, Wentz’s strike to wide receiver Nelson Agholor for the opening score in the Eagles’ 30-17 victory over the Redskins on Sunday probably wouldn’t have warranted tremendous soul-searching.

Instead, it proved a sign of things to come. The Eagles converted 8 of 14 third downs (57 percent) — six coming on third and longs — in handing the Redskins’ their fourth consecutive season-opening defeat under Coach Jay Gruden. (The Redskins’ offense, by contrast, converted just 3 of 11 third downs.)

The Redskins’ third-down defense was a glaring problem amid an otherwise encouraging debut by Greg Manusky’s retooled unit, which kept the team in contention despite four turnovers.

With seven new defensive starters, Washington’s defense held Philadelphia to 58 rushing yards. Linebacker Ryan Kerrigan returned an interception for a touchdown, paring the deficit to 13-7 midway through the second quarter. But at critical junctures, Wentz slipped out of the pocket to complete drive-sustaining throws that kept the score out of reach — including a 12-yard completion on third and 10, a 10-yard completion on third and six and a 30-yard completion on third and 10.

Last season, no NFL team fared worse on third-down defense than the Redskins, who allowed conversions 46.6 percent of the time. That failing went a long way toward explaining the team’s 8-7-1 record.

A survey of NFL teams’ records from 2012 to 2016 showed a notable correlation between third-down defense and overall success. NFL teams that held opponents’ third-down conversions under 35 percent won an average of 9.1 games during the regular season.

Teams that allowed third-down conversion-rates of 35 to 40 percent won an average of 8.4 games. Those that allowed 40 to 45 percent conversion rates won 7.4 games. And teams that allowed 45 percent or higher won an average of 5.3 games.

“At the end of the day, you’ve got the rush the passer,” Gruden said Wednesday, asked about the defense’s poor showing on third down. “You can’t give the quarterback time to throw and set his feet like we did. It’s easy for pro quarterbacks to pick you apart and find an open receiver if they have time.”

Redskins pass-rushers showed speed and power in getting to Wentz. Bringing him down proved tougher, although linebacker Preston Smith notched one sack and Kerrigan combined with Matt Ioannidis for another.

Said nose tackle Ziggy Hood: “We did a great job of getting back there to [Wentz]. He just did an even better job of playing backyard football — scrambling around and making plays with his feet. Give credit to him. It was a tug of war match, and we lost a couple of them.”

By Gruden’s count, four Redskins sacks went wanting as a result.

Gruden said he expects Junior Galette, who was on the field for just 16 defensive plays Sunday, to have a bigger role against the Rams. “We’ve got to ease him back to make sure he’s ready to go,” Gruden said of Galette, a feared pass-rusher when he signed with the Redskins in 2015, only to be sidelined the past two seasons by Achilles’ tears. “He’s going to earn his right and get more and more reps. I think next week you’ll see him probably get 25 reps or 30.”

At 6-5 and 237 pounds, Wentz may be more difficult to topple than the average NFL quarterback. But the Redskins face another big quarterback Sunday in the Rams’ 6-4 Jared Goff.

To rattle Goff, defensive end Stacy McGee said the Redskins’ front must “rush as one.”

Former Buffalo linebacker Zach Brown, whom the Redskins signed in the offseason for his pass-rushing skill, said he doesn’t believe the defense needs to do anything radically different going forward. It just has to do it better.

“We have to just make sure we get the quarterback to the ground,” said Brown, who led the Redskins with 12 tackles, including two for a loss, against the Eagles. “They had him. They were in his face. They had him moving around. The [defensive backs] can’t cover for eight seconds, so that’s really on us. When we don’t get the quarterback down, we feel bad because it’s on us. It’s on us more than on the secondary.”

Former NFL linebacker Chris Spielman, a four-time Pro Bowl selection who will call Sunday’s Redskins-Rams game for Fox, believes the Redskins have enough talent on defense to take a significant step forward this season. He’s impressed with Brown’s playmaking ability. And while he believes the loss of linebacker Trent Murphy to a season-ending knee injury hurt Washington’s pass rush, he thinks talent isn’t an issue, noting the addition of first-round pick Jonathan Allen and the strong first game by Kerrigan.

“Everything is in place,” Spielman said. “Talent-wise, I think they’re fine. It’s not about going out and finding players. It’s about doing it.”