Reserve Jalen Robinson scored all 10 of his points in the second half, including two key 3-pointers in the put-away run, helping Dayton upset No. 17 Saint Louis 72-67 on Wednesday night, the Billikens' third straight loss.
The Billikens (25-5, 12-3 Atlantic 10) still clinched at least a tie for a second straight Atlantic 10 title and the No. 1 seed in the conference tournament anyway when George Washington beat Saint Joseph's 76-71 on Wednesday night.
After the home finale, Saint Louis honored its five senior starters in a low-key ceremony.
Jordan Sibert had 14 points, including three 3-pointers, for the Flyers (21-9, 9-6) while Dyshawn Pierre had 11 points and Devin Oliver had nine points and nine rebounds.
Saint Louis won a school-record 19 straight before getting upset by Duquesne at home last week and then lost at VCU on Saturday.
This is the school's first three-game losing streak since February 2011.
Dwayne Evans had 18 points and nine rebounds and Mike McCall Jr. added 10 points for Saint Louis, which wraps up the regular season Sunday at Massachusetts.
Jordair Jett, who had been averaging 17.6 points in conference play, was held to nine points.
Dayton began celebrating its second victory over a Top 25 team near the end of a 16-2 run that made it 67-59 lead with 3:38 to play.
Robinson had two 3-pointers, Siebert had five points and Oliver capped the run with a three-point play.
Dayton beat then-No. 11 Gonzaga in the Maui Invitational in November.
Saint Louis was 5 for 10 from 3-point range after Jake Barnett connected in the opening minute of the second half for a 42-32 lead - the largest of the game.
But the Billikens made only one of their last 12 from long distance.