Livingston snapped a tie with six consecutive points to give the Patriots (9-9, 3-2 Atlantic 10) an 83-77 lead with a minute to go. Davell Roby responded with a 3-pointer and the Billikens (8-10, 1-4) used their pressure to get a turnover but Saint Louis missed three final 3-point attempts.
Greg Calixte added 11 points for George Mason, which shot 54 percent and made 9 of 20 from behind the arc. Livingston was averaging 26 points over his three previous games and hit that mark while dishing seven assists.
Saint Louis led 39-38 at halftime.
Miami Hurricanes forward Dewan Huell had decided to return for his junior season after pulling out of the NBA draft.
The NCAA has granted Florida State forward Phil Cofer's request for another year of eligibility.
Kansas State's Barry Brown Jr. has withdrawn from the NBA draft and will return to the Wildcats for his senior season.