Thomas, who also grabbed two key rebounds in the final seconds – one off the offensive glass and the other a defensive board – complimented a monster second-half performance from junior point guard Aaron Craft, who totaled 18 of his game-high 20 points after intermission.
Craft connected on 9 of 13 shots from the field, including seven in a row at one juncture, and added a season-high nine assists as well as four steals.
Thomas was the only other OSU player to score in double figures, tallying 16 points. But he struggled with a 6-for-19 performance from the field that included only 2 for 11 from three-point range.
Michigan State (25-8) was led by senior forward Derrick Nix, who totaled 17 points and a game-high nine rebounds. But Nix also made a couple of key mistakes down the stretch, including committing a flagrant foul on Craft as the Ohio State point guard drove the lane with 1:27 remaining in the game.
Craft made only one of the two free-throw attempts to make 58-56 in favor of the Buckeyes, but Ohio State (25-7) retained possession because of the fragrant foul. Sophomore point guard Shannon Scott missed a three-point attempt as the shot clock wound down, but Thomas came up with a huge offensive rebound with 58 seconds remaining.
After an OSU timeout with 32 seconds left, Craft found Thomas on the left wing and the junior rattled home a 14-foot jumper in front of Nix to give the Buckeyes a 60-56 lead with 22.1 seconds showing on the clock.
Michigan State junior guard Keith Appling went for a runner at the other end, but misfired as he was being blanketed by Ohio State sophomore Sam Thompson. The errant shot was rebounded by Thomas, effectively ending the Spartans' chances. Thomas was fouled with 9.1 seconds left, he made 1 of his 2 attempts to make it 61-56, and then MSU freshman Darrell Valentine closed out the scoring with a put-back at the 0:01.0 mark.
The contest was a tight affair throughout with neither team able to gain much of a foothold until late in the second half. Six lead changes marked the first half as each team forged series of mini-runs. The first came from Michigan State, which hit three triples among its first five field goals for a 13-7 lead at the 14:06 mark.
But Ohio State responded by scoring 13 of the game's next 18 points, a run triggered by a dunk from senior center Evan Ravenel off an inbounds pass from Scott. Ravenel also hit a jumper during the spurt while sophomore LaQuinton Ross bagged a pair of threes to give the Buckeyes a 19-15 advantage with 9:42 to play. Ross finished with nine points while Ravenel had six to go along with four rebounds and a pair of blocked shots.
Back came the Spartans with a 6-0 run on two-pointers from Nix, Valentine and Appling to give MSU a 21-19 lead at the 8:11 mark.
After that, it was OSU's turn at another run, this time a 9-2 spurt – seven of the points from Thomas – to give the Buckeyes their largest lead of the half at 28-23 with 4:26 remaining.
But Ohio State went cold from there, missing its last nine field-goal attempts of the half – a couple of them air balls – while Michigan State got back-to-back baskets from Nix and a put-back slam from Payne to take a 29-28 lead into the locker room at the break.
The Buckeyes stayed cold in the early part of the second half, missing four of their first five attempts. But the Spartans couldn't get anything going against OSU's stingy defense.
Ohio State finally got some separation around the 11-minute mark, building a 48-47 lead into a 55-47 advantage thanks mostly to Craft. Ross started the 7-0 run with a free throw before Craft hit three baskets in a row – a layup and two jumpers – to give the Buckeyes an eight-point cushion with 7:23 remaining.
Three minutes later, OSU was still ahead by eight when the Spartans made their last push. Nix connected on one of two free throws to begin a 7-0 run for Michigan State. Appling, who finished with 16 points for MSU, followed with a trey, and after Scott missed the front end of a one-and-one for Ohio State at the 2:10 mark, Nix converted an old-fashioned three-point play.
That made it a one-point game at 57-56 with 1:54 remaining. But the Spartans would draw no closer. Twenty-seven seconds later, Nix reached out and grabbed Craft around the neck from behind to draw the flagrant foul and the Buckeyes were able to close out the victory.
Ohio State advances to the Big Ten tournament title game for the fifth straight time and will meet fourth-seeded Wisconsin, which knocked off No. 1 seed Indiana by a 68-56 final earlier Saturday. Tip time for the championship contest is 3:30 p.m. Eastern.