COLUMBUS, Ohio -- While many outside the program were waiting to see No. 2 Ohio State unveil yet another potent offense against an overmatched opponent, Buckeyes coach Ryan Day was waiting for this -- the game when the passes weren't sailing through the air with precision and ease to future NFL draft picks, when the offense had to grind it out with the running game, and the defense made the difference.

Day got the ugly 21-10 win against No. 5 Notre Dame on Saturday night, and in spite of the sluggish offense, he got something else he was looking for.

"That was something we spent a lot of time in the offseason saying, 'We have to be able to win ugly on offense, we have to stop the run on defense,'" Day said. "They all count the same. And you have to figure out based on who you're going against, how do you want to win that game? When you have that versatility, man, it's going to pay off down the road."

Ohio State's offense, which was No. 1 in the country last year in offensive efficiency, underwhelmed compared to the lofty preseason expectations that pegged the Buckeyes as a strong favorite to finish in the College Football Playoff. With leading receiver Jaxon Smith-Njigba sidelined from an injury he suffered in the first quarter, Ohio State struggled early against a gritty Notre Dame defense.

The Irish, led by popular first-year head coach Marcus Freeman, a former Ohio State linebacker, came into Ohio Stadium and before an announced crowd of 106,594 gave the Buckeyes all they could handle until late in the fourth quarter. Ohio State, which won games last season by an average margin of 29.1 points, was held scoreless in the second quarter and trailed 10-7 at the half.

It wasn't until less than five minutes remaining in the fourth quarter that Ohio State solidified the win -- thanks in large part to a 14-play, 95-yard drive that took 7:06 off the clock and gave the Buckeyes the 21-10 lead.

"We were struggling early on, just trying to get a connection, trying to build that rhythm, but towards the end, we started to get it, started clicking more," said quarterback C.J. Stroud, who completed 24-of-34 passes for 223 yards and two touchdowns. "It's kind of weird being out there again to be honest, seeing the fans, dealing with all of the outside noise, just trying to lock in."

In the fourth quarter, Stroud completed 9-of-10 passes for 107 yards and a touchdown. While it wasn't exactly a splashy Heisman performance, he reminded everyone of his playmaking abilities.

Ohio State entered this season as the No. 2 team after losing to rival Michigan and finishing No. 6 in large part because of the offensive firepower returning from a team that led the nation in scoring and yards per play last year. The Buckeyes have multiple Heisman hopefuls, including Stroud and running back TreVeyon Henderson, but when Smith-Njigba was injured in the first quarter the Buckeyes were off-kilter early. Last year, Ohio State averaged 27.2 points in the first half, the most of any team in the FBS. They had seven Saturday night.

"Early games are a little bit clunky," Day said, "and losing Jaxon threw us off a little bit."

The defense, which was the trouble spot for Ohio State last year, was the highlight on Saturday night. It was a strong debut for first-year defensive coordinator Jim Knowles, who was hired from Oklahoma State. The Irish finished with 253 yards and punted on their last six possessions.

"We were called soft all last year and we had to sit there and just eat," Ohio State defensive back Lathan Ransom said.

Day said the toughness was something the entire team was looking to prove.

"We wanted to be known as something other than just talented," he said.

Notre Dame's game plan was to hold onto the ball, control the clock and keep the Buckeyes' offense off the field. They were able to do that in the first quarter, but finished with only 3-of-13 third down conversions.

Day said he could see more teams trying to do that this fall, but he's not concerned about the passing game moving forward. Ultimately, there were other, lesser-known players who emerged for Ohio State on Saturday night, like former walk-on Xavier Johnson, whose 24-yard touchdown grab put Ohio State up 14-10 late in the third quarter.

"I love these guys," Johnson said, "so with my legs empty, with all that, none of that mattered. It was all for the team and the glory of God. ... I was in position to do what I was coached to do."

In the end they all were -- even if it wasn't pretty.

"It's been a huge emphasis to win this way," Day said. "And it starts with defense. You can play really good strong defense like we played tonight, and we can run the football -- we know we'll throw the ball, we know that -- but if we want to go where we need to be and reach our goals, we need to be able to do those two things."