Bumstead (4-1) turned in his first complete game of the season and the second complete for the Tigers in the South Carolina series. Justin Meier earned a nine-inning win in LSU's 5-1 win over the Gamecocks on Friday.
Sunday's game decided the winner of the series after South Carolina (20-12, 5-7) came back for a win in Saturday's game. LSU has won their past three SEC rubber games and seven consecutive league series dating back to last season
South Carolina scored in its first at-bat for the second game in a row but could not find the necessary pitching to stifle LSU's offense. The first two Gamecocks pitchers lasted less than one inning and set up two bases-loaded situations for the Tigers that produced five runs.
"We set the tone for the game and got their pitcher out of the game before the end of the first inning," LSU coach Smoke Laval said. "That type of pressure was what we were looking for."
LSU took a 12-1 lead into the ninth inning before South Carolina added three runs against Bumstead, who issued his only walk in the Gamecocks' final at-bat. He finished with seven strikeouts and scattered ten hits.
"I just try to get (batters) to get themselves out," Bumstead said. "I don't try to overpower anybody. I jut kind of let my defense play behind me and get things rolling."
LSU answered the Gamecocks' first run in the bottom of the first. The Tigers loaded the bases for cleanup hitter Ivan Naccarata, who hit a two-run single to right field. Clay Harris drove in LSU's third run on a 6-4-3 double play.
South Carolina starting pitcher Matt Campbell (1-3) didn't last through the Tigers' first at-bat, getting pulled after his third walk of the inning.
The Tigers roughed up Campbell's replacement, Zach Reeves, in the second inning with five runs on six hits. And like Campbell, Reeves failed to finish the inning.
Aaron Hill struck the telling blow with a bases-loaded triple down the first-base line. Harris and Blake Gill hit RBI singles for an 8-1 LSU lead.
Harris started a two-out rally in the fourth with a double to the center-field wall and scored when South Carolina second baseman Kevin Melillo let a grounder from Gill go between his legs. Quinn Stewart followed with a home run over the left field bleachers that put LSU ahead 11-1. It was Stewart's fifth round-trip shot of the year.
LSU made it a dozen runs when Matt Liuzza led off the seventh inning with a home run to center field.