Terrence Shannon Jr. shook off a slow start in his return from a concussion, scoring 24 of his 26 points in the second half as Illinois rallied from an 18-point halftime deficit to beat No. 21 Northwestern 66-62 on Thursday night.

Shannon did not start and found himself back on the bench with three fouls as Northwestern (20-8, 11-6 Big Ten) closed on a 13-2 run to take a 37-19 lead into halftime.

But he picked up steam after the break and scored 15 of the Illini's last 24 points as they erased a 14-point deficit in the final 10:07. His tiebreaking drive with 1:16 left put Illinois (19-9, 10-7) ahead 63-61, and he scored the team's last five points - including a pair of free throws that sealed it with two seconds to go.

Boo Buie led Northwestern with a career-high 35 points, hitting six 3-pointers and going 12 of 24 from the floor.

Illinois opened 0 for 11 from 3-point range before Shannon nailed two 3s early in the second half. Matthew Mayer added a 3 and hit three free throws after being fouled during a 14-1 run that winnowed the deficit to four with 15:06 left.

Mayer gave Illinois its first lead on two free throws with 2:36 remaining. He finished with 14 points and eight rebounds.

Buie kept chugging away for the Wildcats after scoring 22 in the first half, including five 3s, by hitting his first four shots after halftime to push Northwestern's lead back to 14.

Illinois climbed into a four-way tie for third place in the conference with three games left in the regular season. Northwestern remains in second but fell two games behind Purdue.

Illinois plays at Ohio State on Sunday.