The Mustangs (8-13, 2-6 Conference USA) fell behind early, trailing at halftime 34-23 and never leading until Walker's 3-point shot with 4:38 remaining put them up 51-50.
SMU then closed the game on a 17-3 run, with Jon Killen scoring on eight free throws and Roberts adding six more points. Killen finished with 11 points and five assists.
Rice (3-19, 0-9) looked like it might get its first conference win and break an 11-game losing streak, building a big lead on 54 percent first-half shooting. But then the Owls missed badly in the second half, going 8-of-28 from the field (29 percent).