Pitts made 7 of 12 shots, including 4 of 6 outside the arc, for sixth-seeded Marshall (21-12), which will play Saturday in its first conference tournament final since the 1997 Southern Conference championship game. The Thundering Herd, which beat Tulsa 105-100 in three overtimes Thursday, will face the winner of Friday's other semifinal between Central Florida and top-seeded Memphis.
DeAndre Kane added 14 points for Marshall, and Dennis Tinnon had 10 points and 13 rebounds.
Southern Mississippi (25-8), the second seed, was led by Angelo Johnson's 24 points. Darnell Dodson added 13.
Marshall shot 54.3 percent (25 of 46), including 9 of 17 (52.9 percent) on 3-pointers. That offset 16 Thundering Herd turnovers, compared to three by the Golden Eagles, who shot 34.2 percent (25 of 73).