The fourth-ranked Vikings (3-1, 0-1 MWC) trailed by as many as seven points in the second half before rallying. Brendan Falls, who finished with a team-high 24 points, hit a 3-pointer with 15 seconds left to force overtime.
The Vikings led 70-66 with 2:02 left on a pair of Dan Evans free throws, but Ripon tied it on Tom Becker's jumper with 52 seconds remaining.
Bo Johnson then hit a jumper with two seconds left to put Ripon ahead. Evans' desperation shot at the buzzer rimmed in and out.
Chris Braier scored 17 points and grabbed 15 rebounds for Lawrence. Becker finished with 29 points for Ripon (4-1, 1-0).