Penn (5-6) leads the all-time series 15-10, but the Dragons (2-8) have won the last six meetings.
Darnell Forman and Antonio Woods hit back-to-back layups to give the Quakers a four-point lead to start OT, but London hit his trey to cut it to one, and then put the Dragons in the lead with two free throws. Kazembe Abif and Allen each added two free throws to preserve the victory.
Allen finished with 16 points to lead Drexel. Abif added 13 points and 14 rebounds.
Woods finished with 17 to lead Penn.