Kevin Walker's first-half goal was the only scoring in USC's 1-0 win over Mercer in the opening round of the NCAA Tournament Thursday afternoon at Stone Stadium.
The win avenged an August 30 loss to the Bears who defeated USC 3-2 in overtime at Stone Stadium.
The Southern Conference champion outshot USC 9-5.
The match was scoreless until the 38th minute Kurtis Turner took a free kick from midfield and delivered it to Andre Street in the box. Street flipped it to Walker who tapped it in for what turned out to be the game-winning goal.
William Pyle did his part in goal for the Gamecocks, recording four saves in the shutout.
Up next for USC is a Sunday trip to Clemson to face the Tigers in the second round.