With 4:04 left in the third quarter Sunday afternoon at MetLife Stadium, Jets linebacker C.J. Mosley was sprinting stride for stride in the middle of the field with Bills wide receiver John Brown. Linebackers aren’t supposed to give blanket coverage on a receiver, but Mosley was in perfect position to break up a deep pass into the end zone.

It was another in what had been a number of brilliant plays by Mosley in his Jets debut. The Pro Bowl free agent from the Ravens had already returned an interception for a touchdown for the game’s first score and also recovered a fumble that stopped a promising Bills drive.

But after breaking up the pass to Brown, Mosley limped off the field with a strained groin. He never returned and the Jets defense was never the same. The Bills would erase a 16-0 deficit by scoring 17 unanswered points to stun the Jets 17-16 in the season opener.

A defense that had forced four turnovers, scored on an interception return and on a safety, couldn’t stop the Bills when it counted as the Jets’ AFC East rival mounted fourth-quarter scoring drives of 85 and 80 yards.

“They know they got away with one today,” defensive lineman Leonard Williams said of the Bills, adding, “It’s demoralizing that you can play that well and still lose a game. It was a just a bad start to the season when you have this game in the bag and it’s a division game that counts as double. We were close to closing this out and have a great start, and we let it slip through our fingers.”

In the midst of a stunned locker room, the Jets wouldn’t blame the defensive collapse on losing Mosley. “Next man up,” is a creed that can’t be doubted. But safety Jamal Adams said the defense went flat late in the game.

“I felt like our energy died and we weren’t playing team ball,” Adams said. “So anytime you do that, a team is going to take advantage of it.”

Five of the Bills’ 10 longest plays came in the fourth quarter, including a 38-yard touchdown pass from quarterback Josh Allen to Brown that gave the Bills the lead with 3:00 remaining. Mosley watched it all from the sidelines, not sure what hurt more — the pain from the injury or watching his teammates lose a game they should have won.

“It was very frustrating,” Mosley said. “It’s always hard when you want to be out there with your brothers and you can’t, especially the way it ended.”

Later he added, “It’s a learning experience for this team. We know in the media, people are going to try to say it’s just like last year. But we control what we control. We’ll go to work Monday and try to get better.”

The Jets had the Bills under control for nearly three quarters. Linebacker Jordan Jenkins ended the Bills’ opening drive by sacking and stripping Allen of the football. Steve McLendon recovered it.

The Bills’ second series turned into a Jets defensive touchdown when Mosley snagged a pass deflected by Bills receiver Cole Beasley and returned it for the first points of the game.

Midway through the second quarter, Allen fumbled the snap on fourth-and-1 and Mosley was there for the recovery. Then on the Bills’ next series, Jets linebacker Neville Hewitt stole a pass intended for wide receiver Zay Jones.

The Jets got their safety in the third quarter when cornerback Brian Poole crushed Frank Gore at the goal line to give the Jets an 8-0 lead, and it was 16-0 minutes later when a 60-yard drive ended with a 9-yard touchdown pass from Sam Darnold to Le’Veon Bell.

Then Mosley got hurt and left the game and the Jets forgot how to play defense.

“I don’t know what it was,” Adams said. “We lost energy as a defense and we didn’t execute. It’s frustrating.”

“Frustrating” was a word spoken often in a Jets locker room, hoping to end a history of not being able to finish games. Instead, a new coaching staff, a new team, a new season, ended with an all-too familiar result