They could, however, make free throws. Sullinger made all 10 of his foul shots in overtime after missing a baseline jumper that would have won the game as time expired in regulation. The Buckeyes attempted just two field goals in the extra period and hit one, a 3-pointer by Jon Diebler -- his only 3 of the game.

Sullinger shot 2 for 12 from the field but 16 of 18 on free throws. His 18 rebounds fell one short of the tournament record set by Ohio State's Greg Oden in 2007.

"With him, when he's not scoring, he's either getting fouled or he'll shoot it and get an offensive rebound and kick it out to one of us," Diebler said.

The Buckeyes scored 12 of their 15 points in overtime at the free throw line. Top-seeded Ohio State, the defending tournament champion, won its fifth straight game to advance to Saturday's semifinals against Michigan.

While the Buckeyes are in line for a No. 1 seed in the NCAA tournament, Northwestern likely needed an improbable run to the conference tournament title to earn its first NCAA appearance.

"We were really hoping to do well at this tournament," said John Shurna, who led the Wildcats with 23 points. "So it's disappointing we won't be -- probably won't be playing in the NCAA tournament, but hopefully it'll be good for our school and for the program to make the NIT."

The Buckeyes, who edged Northwestern by one point in their only regular-season meeting, led 56-55 in overtime when Luka Mirkovic was called for hooking Sullinger while they fought for a rebound.

Mirkovic was issued a technical foul for disagreeing with the call. It was his fifth foul, and Sullinger's primary defender was gone.

"Just in that moment, build-up or no build-up, in that moment he certainly didn't do what he should be doing," Northwestern coach Bill Carmody said.

William Buford missed both technical free throws, but Sullinger made his two foul shots to give Ohio State a 58-55 lead. The Buckeyes maintained control by going 6 for 6 from the free-throw line the rest of the way.

Aaron Craft scored 17 points and Diebler added 13 for the Buckeyes (30-2).

Michael Thompson scored 15 points and Drew Crawford had 12 points and 10 rebounds for the eighth-seeded Wildcats (18-13). Thompson was coming off a tournament-record 35 points in Thursday's win over Minnesota.

Ohio State shot 32.2 percent from the field, matching its worst effort of the season, but outrebounded the Wildcats 48-27.

Diebler, who had made 17 3-pointers in his previous two games, went 1 for 5 from beyond the arc against the Wildcats. The Buckeyes were 3 of 15 on 3s.

"There's going to be games where we go 40 percent from 3, 50 percent, and there's going to be games where we go 3 of 15," Diebler said. "I think the one positive is that we did a lot of things well besides just feeding inside. We really did a good job of opening up driving lanes and attacking the glass."

The teams battled back and forth in the second half until the final minute. With the score tied at 52, Northwestern had a chance to take the lead, but David Lighty blocked Crawford's jumper. Then Sullinger's shot fell short as time expired.

"It slipped out of my hand as I was trying to make the move," Sullinger said. "I realized how much time was left, and I didn't want to give us just one shot, I wanted to give us multiple shots like we did in the first half."

Shurna's shooting kept Northwestern in the game early in the second half, and Thompson's short jumper with 10:54 remaining gave Northwestern a 38-37 lead.

Ohio State couldn't hit early, and Northwestern took advantage. Shurna made a 3-pointer to give the Wildcats a 16-14 lead with just under 7 minutes left in the first half.

The Buckeyes missed 21 of their first 31 shots, but Craft hit a 3-pointer, then a layup to give the Buckeyes a 26-23 lead in the final minute of the first half. After frantic action near the basket, Craft's tip-in at the buzzer gave the Buckeyes a 28-23 lead at the break.

Ohio State won 58-57 at Northwestern on Jan. 29. In the two meetings, Sullinger said Northwestern earned his respect.

"Northwestern, they have crazy discipline," he said. "I can't even explain it. They run their offense, nobody tries to make great plays, nobody tries to go out of the ordinary. They stay consistent with their system, and that's what makes Northwestern so hard to play and makes them so good."

Northwestern didn't feel good about just being close in either game.

"I think we have a good team, so you'd like to win those games, and you could see it from the guys," Carmody said. "They came here to win and thought they could, and we were right there."