Quarterback Kirk Cousins. (John McDonnell/The Washington Post)

Washington’s first-string offense was approximately as sharp as a toddler’s play knife early on Friday night. Quarterback Kirk Cousins underthrew one receiver deep, underthrew another receiver in the flat and missed a third receiver over the middle. He threw one interception that counted, one that was called back by a penalty, and another hopeful ball that was tipped dangerously into the air. Steady receivers dropped passes, and veteran offensive linemen committed penalties. There are faucets underneath RFK Stadium with less apparent rust.

“Obviously we didn’t come out the way we wanted to,” Coach Jay Gruden said. “Wasn’t as crisp as I would have liked to have seen it.”

And so now go ahead and nervously peer at Cousins’s final numbers in his final half of preseason action. How’s 12 for 23 for 188 yards and three touchdowns sound? If that’s the rusty version of Washington’s offense, the polished version might resemble, say, the outfit that ripped up the franchise’s passing record book last season.

Yes, this performance came against not just the Buffalo Bills defensive backups, but the backups’ backups. (The Bills benched five starters and removed the rest of their first-string defense before the first quarter ended. Please ban preseason football.) Yes, Buffalo helped considerably by committing one penalty after another, leading to a first half that lasted about two hours, not even counting Ed Hochuli’s speeches. And yes, as always, conclusions drawn from preseason games are worth as much as those Haynesworth, Landry and Stubblefield jerseys that filled the stands at FedEx Field. (All of us who attend these things have problems. Some more than others.)

I’ll risk a few conclusions anyhow, having watched this final preseason showing from Washington’s first-string offense in a 21-16 win: There will be plenty of open receivers this season, even when the opponent is not Buffalo’s third string. Cousins’s right arm will not grow flabby from lack of use. Announcers won’t need that old saw about “taking the air out of the football,” unless they’re making jokes about the Patriots. And that reliable crew of “Run the ball!” sports-radio callers might need oxygen tanks.

Washington ended last season flinging the ball all over the field, and it came out on Friday doing the same thing. Counting plays that were nullified because of penalties, nine of the Redskins’ first 11 plays involved Cousins dropping back to pass. The team’s top two running backs — Matt Jones and Chris Thompson — were both out with injuries, but this still felt like the Jay Gruden and Sean McVay show from last season, when Washington finished sixth in yards-per-passing-attempt and 30th in yards per rushing attempt.

The thing is, a quick-strike West Coast passing offense looks explosive when it’s working, and amateurish when it isn’t. Gruden barely used Cousins in the first preseason game, and chose to bench most of his first-stringers last week, a bit of confidence that some critics saw as unwarranted hubris.

The first-string offense had therefore played one series in eight months entering Friday night. It looked like it. Cousins ended the first quarter 3 for 9 with 17 yards, an interception and a few striking missed connections. He wasn’t helped by his receivers: Jordan Reed and Pierre Garcon both had drops and several potentially great catches fell to the ground. Cousins and his receivers seemed off and cynics might have wondered if this was a $20 million quarterback.

“There were moments where it wasn’t as good as it needs to be, and we know that,” Cousins said.

The second-year starter though, can’t try to justify his riches every time he takes the field. And he especially can’t do that during August practices, or in preseason exhibitions. He’s talked repeatedly about taking advantage of his first steady NFL job to experiment a bit: trying risky throws in practice to see what he can and can’t get away with, and fine-tuning his game without worrying whether a coach might be judging his every move.

“As a starting quarterback, I think you want to be really sharp, but . . . in training camp you’re not trying to necessarily be ready to go for the first preseason game, you’re trying to be ready to go for Week 1,” Cousins said this week. “So you’re trying to build everything towards Week 1 a little bit more than when you’re fighting for that backup spot.”

This wasn’t Week 1, so it was still part of the build. Thus, Cousins’s second ball on Friday was a bomb to Garcon that landed yards away from the wide receiver. Later, he tried to find DeSean Jackson deep down the sideline, underthrowing his mark, and Jackson’s second foot landed out of bounds. In the first half, Washington ran twice as many passing plays as rushes.

Cousins said he checked out of some run plays into passes, and that the team will have more success if he throws between 20 and 30 passes a game, even if that hurts his stats. Maybe that’s the case.

But it’s also easy to imagine that this offense will go as far as its pass catchers — and quarterback — can take it. Garcon and Jackson both rank in the top 18 of wideout receiving yards over the past seven seasons. Vernon Davis is sixth among tight ends in that span — and he’s Washington’s backup. The starter, Jordan Reed, showed again Friday his disdain for linebackers in coverage; no one was near him on his touchdown grab. Jamison Crowder, who didn’t play Friday night, finished fifth in receptions among rookie receivers last year. And then the Redskins used their first-round pick on another wide receiver, Josh Doctson, who hasn’t even played yet.

With some of those weapons finally clicking in the second quarter of this pretend game, Cousins went 9 for 14 for 171 yards and three touchdowns — a game’s worth of production. He got those numbers not through individual brilliance but by operating this precision offense: a short ball that Jackson took 39 yards, a quick strike that Grant turned into a 38-yard touchdown sprint, a nimble little nine-yard fade to Garcon in the end zone. So much for rust.

“It’s gonna be a four-quarter game for the 16 that we play this season,” Cousins said. “We’re gonna have slow moments or slow quarters at times, and the key is going to be to find a way to circle the wagons and regroup so that by the end of the four quarters we’ve put together a good performance. And certainly in the time we had tonight, the body of work overall was pretty productive.”

Considering the opposition, maybe anything less than that would have been concerning. And it already feels like every game this season will be a referendum on the quarterback: whether he was worth this massive raise, whether he deserves another one, whether last year was a fluke.

Friday night was the most important data point of this preseason. And even if it didn’t mean much, it hinted at what Cousins and his pass-catchers can do. There will be plenty of open receivers, and plenty of chances to deliver them the ball. That won’t matter if Cousins struggles. But a sharp quarterback — more steak knife than the toddler variety — and no one will worry about Dan Snyder’s $20 million.