Smith scored a season-high 24 points, Thomas added 19 and No. 16 Ohio State used a late run to beat Northwestern 63-53 on Thursday night.
The Buckeyes (21-7, 11-5 Big Ten) moved one-half game ahead of Michigan and took sole possession of fourth place in the Big Ten with another difficult win over a team that's given them fits in recent years.
This time, they led by 11 points early in the second half and regrouped after Northwestern took the lead, sending the Wildcats (13-16, 4-12) to their sixth straight loss and eighth in nine games.
"I give them tremendous credit, with all the injuries they've faced," Ohio State coach Thad Matta said. "They've kind of been knocked down a couple times."
Northwestern lost two of its best players -- Drew Crawford and Jared Swopshire -- to season-ending injuries and that was after guard JerShon Cobb was suspended for the season for violating team policy. It's added up to a difficult season, but the Wildcats again found a way to make the Buckeyes sweat.
Northwestern led by a point twice in the second half and was up 49-48 with about 4 minutes remaining after a 3-pointer by Reggie Hearn. But Ohio State outscored the Wildcats 15-4 the rest of the way.
Thomas scored six points during that stretch, and the Buckeyes took advantage of three straight turnovers to come away with a tight win.
Smith scored 14 points in the first half and had five of Ohio State's 10 field goals, including four 3-pointers, as the Buckeyes grabbed a seven-point lead. He was 7 of 13 overall and hit 6 of 11 3s in the game, and the Buckeyes avoided another Big Ten upset after No. 1 Indiana lost to Minnesota and Penn State upset No. 4 Michigan this week.
They also took a step toward a first-round bye in the conference tournament. Securing one won't be easy with a trip to Indiana next week and home game against Illinois looming, but the Buckeyes did what they had to do in this one after squeezing by Northwestern two weeks earlier.
"When me and Deshaun are both connecting on the offensive end I feel like we're a very dangerous team," Smith said. "Obviously we have the second option when I'm going and then we get other guys going."
"It was a lot of fun to play in a competitive game, but that's not what we play for," Sobolewski said.
The Wildcats have lost eight straight and 19 of 20 against Ohio State, but the lopsided record aside, recent games have been close -- particularly at Welsh-Ryan Arena.
A year ago, the Buckeyes needed Jared Sullinger's banked turnaround with 3.1 seconds left to escape with a 75-73 win. In 2011, they were 22-0 and No. 1 in the nation, but they barely won, 58-57, with David Lighty making a late steal and Sullinger hitting a free throw.
The game at Value City Arena this season was anything but a breeze, with Northwestern in control most of the way before Ohio State put together a late 12-point run to pull out a 69-59 victory.
This one wasn't easy, either.
Ohio State was leading 33-22 early in the second half when Northwestern went on a 12-3 run, with Demps nailing a 3 and scoring on a backdoor layup and hitting two free throws to make it a two-point game with 15:32 remaining.
Northwestern took its first lead of the game midway through the second half when Kale Abrahamson hit a 3 to make it 41-40.
Thomas scored on a tip-in and Smith hit a 3 to make it 45-41, but the Wildcats hung in, tying it at 46 on Alex Olah's three-point play with 6:31 left.
After Thomas scored on a bank shot, Hearn put Northwestern ahead again with a 3, but Smith answered with one to make it 51-49, Ohio State.
Smith stripped Demps, but Thompson missed two free throws.
Another turnover by Northwestern led to a layup by Thomas to make it 55-49, and Thomas scored again on a nice spin move with 1:24 left to get the lead back to six after Olah scored for Northwestern.
"He pressed a little bit, especially in the first half tonight because they were converging on him," Matta said. "I thought he did a really nice job down the stretch of finding the seams."
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Mississippi State freshman guard Malik Newman will withdraw from the NBA draft, but sources told ESPN he might explore other opportunities besides returning to Mississippi State.
Seton Hall sophomore Isaiah Whitehead will stay in the NBA draft and not return for his junior season.
Washington State's trio of Josh Hawkinson, Conor Clifford and Ike Iroegbu have withdrawn from the NBA draft and will play their senior season with the Cougars.