Bassey was 3 of 4 from 3-point range with a pair of 3s late in the second half that helped to force overtime. The Crimson (15-11, 10-1) stayed tied with Pennsylvania (10-1), which beat Dartmouth on Friday night.
Harvard scored the opening basket of overtime and never trailed, starting the period with a 10-2 run.
Myles Stephens, who finished with a career-high 33 points for Princeton (11-15, 3-8), scored all six of the Tigers' points in overtime.
The Crimson forced overtime without holding the lead for the last 38 minutes of regulation. The Tigers had their largest lead at 41-31 after a 14-4 run.
Chris Lewis added 13 points and Danilo Djuricic scored 12 for Harvard.
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