Baylor (20-1) rallied from a 15-point deficit in the first half to win its fifth straight game. The Bears trailed 50-40 early in the second half, but pushed ahead to take their first lead at 56-54 with 10:25 left after Motley made a pair of free throws.
It was a close game from that point forward. Lecomte hit a decisive 3-pointer with 23 seconds left that made it 78-72 and sent many of the Ole Miss fans to the exits.
The 5-foot-11 Lecomte shot 6 of 9 from the field, including 5 of 6 from 3-point range.
Ole Miss (12-9) dominated early on and jumped out to a 33-18 lead with 6:33 remaining in the first half. Sebastian Saiz and freshman Breein Tyree both scored 20 points for the Rebels. That was a career high for Tyree.
Baylor: The Bears struggled, especially when Motley was in foul trouble during the first half, but surged ahead late to escape Oxford with the win. Now they've got another tough road game at Kansas on Wednesday.
Baylor travels to face No. 2 Kansas on Wednesday.