ANN ARBOR, Mich. — Another year, another first in the Ohio State-Michigan rivalry.

Last year, the teams played their first overtime. On Saturday, the drama — and mystery — began before the Buckeyes’ first snap.

During Michigan’s opening possession, an unidentified person bumped into Ohio State quarterback J.T. Barrett’s knee on the sideline, causing swelling that would eventually contribute to him leaving the game in the third quarter with the Buckeyes trailing by six.

But in the first pressure-filled situation of his college career, Dwayne Haskins Jr. was up to the challenge. The redshirt freshman played flawlessly in directing scoring drives on his first two possessions as the Buckeyes rallied for a 31-20 victory in front of 112,028 at Michigan Stadium.

No. 9 Ohio State (10-2, 8-1 Big Ten) kept alive its College Football Playoff hopes heading into next week’s Big Ten championship game against Wisconsin. The Buckeyes have won 13 of their last 14 against Michigan (8-4, 5-4) and stayed undefeated in six games against the Wolverines under Urban Meyer.

But the Ohio State coach was more livid about the circumstances of Barrett’s injury than happy with the victory or Haskins’ clutch performance. He blamed himself, apparently for not ensuring that the Ohio State sideline was cleared of non-Buckeyes.

“A guy with a camera hit him in the knee,” Meyer said. “I’m going to find out who. I’m so angry.”

Barrett said his knee was OK for a while, but Ohio State wasn’t. A 12-point underdog, Michigan dominated the first quarter.

With much-maligned John O’Korn playing in place of the injured Brandon Peters at quarterback, the Wolverines put together one long touchdown drive and got a punt return to set up another score for a 14-0 lead one play into the second quarter.

After being held to minus-6 yards in the first quarter, the Buckeyes’ offense finally awoke in the second and Ohio State tied the game at 14 by halftime.

Michigan regained the lead with a touchdown midway through the third quarter, though Denzel Ward blocked the extra point to keep it 20-14.

On the Buckeyes’ next possession, Barrett rolled out and ran for a 10-yard gain. He got up slowly, then went back to the turf, holding his right knee.

Barrett later revealed that he has been dealing with a meniscus issue all season, but that when his knee twists, he can pop it back in place. He couldn’t this time, however, because his knee had swollen from the sideline mishap.

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Enter Haskins, whose seven appearances this year had been in a mop-up role.

“It was really unreal,” he said. “The first person you’d think would be nervous (would be me), and honestly I wasn’t. I had the O-line and the receivers and everybody behind me.”

Haskins has a big arm, and he showed it with a 27-yard completion between two defenders to Austin Mack; the throw came on third-and-13 and followed two false-start penalties. Two plays later, Haskins scrambled for 22 yards to the 1 to set up a touchdown run by J.K. Dobbins. Sean Nuernberger’s extra-point gave Ohio State its first lead, 21-20 with 1:34 to go in the third quarter.

After a defensive stop by the Buckeyes, Haskins threw to K.J. Hill for a 29-yard completion on a drive that ended with a 44-yard field goal by Nuernberger to make it 24-20.

Nuernberger would miss a 43-yard field goal with 2:47 left to give Michigan one last attempt. But Jordan Fuller intercepted a badly overthrown pass by O’Korn, the last of his several misfires. O’Korn finished 17 of 32 for 195 yards.

Ohio State running back Mike Weber ended any doubt about the outcome with a 25-yard touchdown run with 1:44 left.

“It was a street fight, and we hung in there and found a way to win,” Meyer said.

Haskins completed 6 of 7 passes for 94 yards after Barrett was only 3 of 8 for 30 yards.

“It’s crazy to go win in the biggest rivalry in sports,” Haskins said. “I never thought it would be a reality. I’m just always preparing in meetings and asking questions, and it all worked out for me.”

It was the second time in four years that Barrett couldn’t finish a Michigan game. In 2014, Barrett broke his ankle on the first play of the fourth quarter. Cardale Jones then led the Buckeyes to the College Football Playoff championship.

Barrett said this injury isn’t serious and that he will be able to play against Wisconsin. But Haskins showed he is capable if Barrett can’t go.

brabinowitz@dispatch.com

@brdispatch