Thomas' string of points put UMass Lowell ahead with 1:20 to go.
Cornell was within three, 77-74, after Robert Hatter's basket with 17 seconds left. Keith Hayes II responded with a pair of free throws for the River Hawks before Cornell's Matt Morgan sank a 3-pointer to make it 79-77 with five seconds remaining. Hayes added a final free throw before Morgan missed a 3-pointer.
Morgan finished with 23 points, Hatter 14 and Troy Whiteside 10 for the Big Red (3-4).