Barrett connected five times from 3-point range for the Tigers (6-7), who were 6-for-8 behind the arc in the first half and led 41-32 at the break.
Hummer scored 16 first-half points, and the senior forward moved into seventh place on Princeton's career scoring list with 1,381, passing Bob Scrabis (1985-89). Hummer made 10 of 16 shots in the game.
Jack Isenbarger scored 16 points and Lucas Troutman 14 to pace Elon (8-6), which never led. The Phoenix won 56-55 at Princeton last season and had beaten their two previous Ivy League opponents this season, Dartmouth and Columbia.
Isenbarger made two 3-pointers to move into a tie for fifth with Chris Long (2007-11) on Elon's career list with 172.
Mike Krzyzewski says he has good reason to be excited for next season thanks to a combination of Duke's incoming freshmen and a core of experienced upperclassmen.
Georgia guard Juwan Parker has been awarded a medical redshirt, leaving him with two years of eligibility, after missing the 2015-16 season with a partially torn Achilles tendon.
Forward Trevon Bluiett has withdrawn from consideration from the NBA draft and will return to Xavier for his junior season.