Ohio State (17-13, 9-10 Big Ten) has won consecutive games since ending a three-game skid. Nebraska (17-13, 7-12) has lost four straight and five of its last six.
Parrish shot 5 of 11 from long range and finished with 22 points. Devin Royal also scored 22 points for the Buckeyes. John Mobley Jr. added 20 points and Sean Stewart chipped in with 13. Thornton and Mobley each made three 3s.
Williams made five 3-pointers and finished with a career-high 43 points on 16-of-29 shooting to lead Nebraska. Juwan Gary added 24 points, Connor Essegian had 16 and Andrew Morgan 14.
Ohio State led by as many as 11 points early in the second half, but Nebraska ended regulation on a 9-2 surge to force the first extra period tied 89-all. Thornton and Parrish each hit a 3-pointer in a 7-2 closing spurt to force a second overtime knotted at 99.
Ohio State plays at Indiana on Saturday and Nebraska hosts Iowa on Sunday in regular-season finales.
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