The Tigers (13-6, 4-1 Conference USA) trailed 36-35 with 13 minutes to play, but outscored the Mustangs 19-2 over the next 11 minutes to pull away.
During a stretch of the second half, SMU (10-9, 2-3) connected on only 2 of 18 shots to help Memphis build a double-digit lead.
Memphis controlled the boards 36-27, including 13 off the offensive glass, leading to 14 second-chance points.
Memphis had 9-point lead, 30-21, in the first half but SMU closed out the period with seven straight points to lead 30-28 at the break.
Seton Hall sophomore Isaiah Whitehead will stay in the NBA draft and not return for his junior season.
Washington State's trio of Josh Hawkinson, Conor Clifford and Ike Iroegbu have withdrawn from the NBA draft and will play their senior season with the Cougars.
Gonzaga center Przemek Karnowski, who missed most of last season with a back injury, says he is returning for another year.