Russell's 3-pointer with 3:34 to play snapped a 60-all tie, which answered the 3-pointer of Northwestern's JerShon Cobb that created the deadlock. Russell's sixth 3-pointer of the night made it 66-60 with 1:36 to play.
Northwestern's Tre Demps hit a 3-pointer to pull the Wildcats within a point with 1.8 seconds to play, but Russell's free throw in the final second sealed the outcome.
Ohio State (14-5, 3-3) used a 16-7 run early in the second half to expand its lead to 11 points. A pair of 3-pointers from Russell, plus a jam from Sam Thompson (11 points), helped them pull away. Russell also pulled down seven rebounds and had six assists.
Ohio State, which trailed by 11 points after nine minutes, bounced back from Saturday's loss at Iowa, while Northwestern dropped its fifth straight.
Northwestern closed the gap to 56-54 behind 3-pointers by Dave Sobolewski and Olah, but a pair of jumpers by Russell pushed Ohio State ahead.
The Wildcats had jumped to a 21-10 lead before Ohio State could get untracked. Four offensive rebounds in that stretch helped the Wildcats build the advantage, with Olah scoring three of the Wildcats' first five baskets.
A pair of 3-pointers by Russell kept Ohio State in contact, and his 16-footer from the wing triggered a 10-point run for Ohio State, which outscored Northwestern 28-13 the rest of the first half. Russell, selected as the Big Ten's freshman of the week three times this season, had 12 points in the first half.
Ohio State: Coach Thad Matta's 125th victory in Big Ten conference play tied him with Tom Davis of Iowa for 15th in league history.
Northwestern: The 11-point lead the Wildcats built in the first nine minutes was their largest of the season in Big Ten play.
Ohio State hosts Indiana on Sunday.
Northwestern makes its first visit to Maryland for a conference game on Sunday.