The Flyers (11-5, 1-2) were led in scoring by Nate Santos, who finished with 18 points. Javon Bennett added 17 points and Zed Key finished with 16 points.
Rivera scored nine points in the first half and UMass went into the break trailing 39-36. UMass went on a 12-2 second-half run erased to give them the lead at 63-58 with 6:10 remaining. Rivera scored 14 second-half points.
Both teams play George Mason next, UMass on the road on Saturday and Dayton at home on Jan. 15.
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The Associated Press created this story using technology provided by Data Skrive and data from Sportradar.