The 11th-ranked Lady Buffs rolled to a 30-28, 25-19, 25-19 win to improve to 24-4 on the season and to 14-3 in league play.
The loss eliminates the Mustangs from LSC Postseason Tournament consideration as MSU dropped to 6-22 on the season and to 4-14 in the conference loop.
Stewart shined from the outside putting down a team-high 11 kills while committing a single error for a .323 attack percentage, while Wallace provide the inside muscle with 10 kills and three errors to hit .269.
The Mustangs battled for two set points in the opening frame before falling 30-28.
West Texas A&M used a balanced attack led by Halie Harton and Stormi Lancaster who put down 11 kills each while Kameryn Hayes added 10 kills. Lexi Davis and Erin Dougherty added nine kills each.