The sixth-seeded Thundering Herd (19-12) led 33-26 after DeAndre Kane scored 11 of his 18 points in the first half. But Marshall went scoreless for the first 4:29 of the second half as the 11th-seeded Mustangs (13-19) tied it 33-33 on a Jeremiah Samarrippas jumper with 16:09 left.
A jumper by Pitts ended the drought, and Shaquille Johnson scored seven points during an 11-2 run that gave the Thundering Herd a 44-35 lead with 10:48 remaining.
Rodney Clinkscales led SMU with a season-high 17 points. Robert Nyakundi, whose 42.5-percent 3-point shooting led the conference, made just 2 of 10 - and the Mustangs 6 of 24 - from long range.