Ohio State couldn’t have played better at the start of its season opener Saturday.

That might have been the problem.

The Buckeyes scored four quick touchdowns against Florida Atlantic to look every bit a team with unlimited potential. The rest of their 45-21 victory showed how much work they have to do to reach that potential.

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Even so, the announced crowd of 103,228 at Ohio Stadium had plenty to please them in the debuts of Justin Fields at quarterback and Ryan Day as full-fledged coach.

Fields, the much-touted transfer from Georgia, ran for a 51-yard touchdown on his first carry and threw for four touchdowns.

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The first three touchdown passes came in a span of less than five minutes to tight end Jeremy Ruckert and receiver Binjimen Victor, both of whom were wide open, and then to Chris Olave. That made it 28-0 with 6:50 left in the first quarter. It looked like Ohio State would be able to name the score.

“I don’t know if I’ve been in a game like that,” Day said of the early onslaught. “It was kind of strange. We came out to such a quick lead, and maybe we took a deep breath there, I’m not sure. But we can’t let that happen.”

After the fourth touchdown, Ohio State’s offense went into an extended funk. Running lanes disappeared and the pass protection faltered.

The Buckeyes defense, though, was suffocating for the entire first half. The Owls had minus-14 yards in the first two quarters. The Buckeyes stuffed them for negative yardage on 11 of FAU's 32 first-half snaps.

The Owls didn’t have the ball in Ohio State territory until they recovered a J.K. Dobbins fumble at the 25-yard line and kicked a field goal just before halftime.

“Especially in the first half,” defensive co-coordinator Jeff Hafley said, “I was really proud of those guys. I think the way we ran to the ball, at least from upstairs (in the coaching booth), it looked like there were seven guys around the ball carrier on every single play.”

It was more impressive because the Buckeyes were without three of their defensive ends. Starter Jonathon Cooper and backups Tyreke Smith and Tyler Friday were out because of injuries. That caused Jashon Cornell to move from defensive tackle to end opposite Chase Young.

The defense wilted some in the second half, especially when backups filtered in. Florida Atlantic scored two touchdowns in the fourth quarter.

“Our second team came in and let them come down the field, and we can’t have that,” Day said. “We have to play with depth this season, so (there’s) a lot to learn from.”

The same goes for the offense. It didn’t reignite until late in the third quarter when Fields threw another touchdown pass to Ruckert to make it 35-6. The Buckeyes added a final TD when Dobbins scored on a 1-yard run early in the fourth quarter.

Fields completed 18 of 25 passes for 234 yards. After the touchdown run, he didn’t do much as a runner, finishing with 61 yards on 12 carries, which includes two sacks for minus-23 yards.

But overall, it was a successful debut. Fields was the No. 2 overall prospect in the 2018 recruiting class. After spending his freshman season as a backup at Georgia, he enrolled at Ohio State in January.

Since then, he has taken a crash course in trying to learn Day’s complex offense. There were a few plays he’d like to have back, but he didn’t come close to throwing an interception and was accurate on most of his throws.

“All aspects of my game can get better,” Fields said. “I’m just going to get back in the film room and see what mistakes we had and fix those and get ready for Cincinnati.”

Coach Luke Fickell’s Bearcats will provide a tougher test next week. But Day wanted to savor this victory. He served as Ohio State’s coach the first three games last year during Urban Meyer’s suspension, but now the Buckeyes are his team.

He took a moment before running on the field from the tunnel to appreciate the moment.

“It’s unbelievable,” he said. “The hair stands up on your arms and on the back of your neck, and you really feel fortunate to be in that situation.”

He no doubt felt even better midway through the first quarter before it became apparent that the Buckeyes aren’t yet a finished product.

brabinowitz@dispatch.com

@brdispatch