The freshman forward, who shot 12 of 14, had 21 first-half points to help the Trojans go up 52-43. He scored 53 points and grabbed 28 rebounds during the three-game event.
Jonah Mathews and Quinton Adlesh both added 12 points for USC (7-2), which used its size to take control during a second half where the Trojans took a 25-point advantage with nine minutes left.
Noah Kirkwood had 12 points for Harvard (5-4). Bryce Aiken, who averaged 22.5 points over the first two games of the tournament, had 10.
USC shot 49.2% (30 of 61) and outscored Harvard 36-20 in the paint.
Harvard was 21-57 (36.8%) from the floor and was outrebounded 42-28
USC rebounded from after losing 101-79 to Marquette on Friday. The Trojans were unable to contain Golden Eagles guard Markus Howard, who set a tourney record with 51 points.
Harvard played the role of preseason top pick in the Ivy League media poll announced by the league in October. The Crimson, which beat Texas A&M 62-51, and led No. 5 and eventual invitational champion Maryland by four at halftime before losing 80-73 earlier in the tournament, wore down during the second half Sunday.
USC is at TCU on Friday night.
Harvard will be at home Saturday against Massachusetts.
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Okongwu puts on dunk show in USC's win vs. Harvard
USC freshman Onyeka Okongwu has a dominant effort against Harvard, tallying 27 points and 14 rebounds in the Trojans' 77-62 win.