Illiniois' Malcolm Hill lost the ball near the Buckeye basket, Keita Bates-Diop came up with it and fed Mickey Mitchell, who loped to the other end of the court for an easy layup with four seconds left that locked up a 68-63 win.
''I'm still trying to figure out how Mickey Mitchell came out of there with that basketball,'' Ohio State coach Thad Matta said. ''I've never seen anything like it. I'm glad he did.''
The end may not have made much sense to Matta, but the win was tough to figure out, too.
Both teams played sloppy. Ohio State (14-8, 6-3 Big Ten) hit 39 percent of its shots and Illinois just 32 percent.
''It wasn't always pretty, but both teams were going at it,'' Illinois coach John Groce said.
Trevor Thompson, who led Ohio State with 16 points, acknowledged that a month earlier the young Buckeyes might not have come out of the game with a win.
''I feel like we've definitely grown up,'' he said.
JaQuan Lyle hit a pair of free throws, his only points of the night, with 14 seconds left in overtime to put the Buckeyes up 66-63 before Mitchell iced the game.
The Illini (10-11, 2-6) trailed by 13 with 6:34 to play but fought back and tied the game at 58-58 on a 3-pointer by Jalen Coleman-Lands with 56.9 seconds left in regulation.
But Illinois scored just five points in overtime.
Bates-Diop finished with 15 points and 12 rebounds for Ohio State and Marc Loving scored 11 with 10 boards.
Kendrick Nunn led Illinois with 24 points, including five 3-pointers.
The Buckeyes used a big offensive rebounding edge, 13-5, to put away a dozen second-chance points. Illinois had just four.
In all, the Buckeyes grabbed 51 rebounds to Illinois' 34.
And the Illini were 18-31 from the free throw line.
Illinois opened the game with a 13-2 lead. But the Illini had just one field goal, a jumper by Nunn, between the 11:25 mark of the first half and halftime.
Hill finished with 12 points for the Illini and Coleman-Lands 11.
Ohio State's Jae'Sean Tate fouled out in overtime. He finished with nine points.
Illinois' fast start was fueled in part by a pair of buckets by Nunn from the corner in front of the Ohio State bench. They put an early scare in Matta.
''The scouting plan was try not to let him get going,'' Matta said. ''When he made those, I thought, `Oh boy.'''
Official Ted Valentine is a regular target for members of Illinois student section, the Orange Krush. Thursday, he returned the favor. During one lengthy video review, one student yelled ''It shouldn't be that hard!'' at Valentine. ''Whoa!'' the veteran ref barked back, giving the student a hard stare.
Ohio State: The Buckeyes were 7 of 13 from the free throw line. The Buckeyes went to the line 39 times in their last meeting with Illinois, hitting 28 in a 75-73 win in Columbus on Jan. 3 ... Matta made the most of his trip Champaign, offering Michael Finke's little brother, Tim Finke, a scholarship. Tim Finke is a sophomore guard at Champaign Central and is highly regarded.
Illinois: Coming into Thursday's game, Illinois had lost its last five games against Ohio State and 11 of the last 13. ... Hill and Nunn, who came into Thursday's game averaging 18.7 and 17.5 points a game, respectively, are one of only two pairs of teammates in the country averaging at least 17 points a game each. Duke's Grayson Allen (20.3) and Brandon Ingram (17.1) are the other two.
Ohio State: Hosts No. 8 Maryland on Sunday.
Illinois: Hosts Wisconsin Sunday.