McLouth Reed Grabill scored 27 points, and Seabury defeated McLouth, 53-50, for its first victory ever in the McLouth Invitational.
Bill Gibbs had 14 points for Seabury.
Skyler Malone added seven points, and Dan Simons scored five.
The Seahawks overcame a six-point deficit in the fourth quarter after switching from a zone defense to man-to-man for the first time this season in the final three minutes.
“We gutted it out,” Seabury coach Mike Harding. “We went man-to-man and got a lot of turnovers.”
Seabury (5-1) will play Jefferson North at 6:15 p.m. Friday in the semifinals at McLouth.