The win clinched an SEC series victory for LSU (31-17 overall, 10-13 SEC), which has captured four of its last five conference series.
LSU is now in sole possession of ninth place in the overall SEC standings, one game behind eighth-place Mississippi State (11-12) with seven league games remaining. The top eight teams qualify for the SEC Tournament May 24-28 in Hoover, Ala.
Auburn dropped to 22-27 overall, 9-14 in the SEC with Saturday's loss.
The teams meet in the series finale at 1 p.m. Sunday. Junior left-hander Daniel Forrer is LSU's scheduled starting pitcher while Auburn is expected to counter with junior right-hander Chris Dennis.
"Louis Coleman gave us another good outing tonight," said LSU coach Smoke Laval, "and Will Harris was outstanding in relief. We competed well, had some good fortune and came up with some timely base hits."
Coleman (5-3) limited Auburn to three runs on six hits in six innings with two walks and five strikeouts. Harris fired three scoreless innings to earn the save, allowing just one hit with no and a career-best four strikeouts.
LSU catcher Matt Liuzza broke a 3-3 tie in the sixth inning when he led off with a home run against Auburn starter Evan Crawford (5-6). The homer was the third of the season for Liuzza, who was 3-for-4 on the night with one RBI and two runs scored.
"Matt has taken a strong leadership role on this team," Laval said. "He really has become our ‘go-to' guy down the stretch. He's hitting the ball right on the nose right now."
The Tigers added an insurance run in the ninth inning as Harris – who started the game at third base – walked and later scored when Auburn shortstop Justin Bristow misplayed J.T. Wise's two-out grounder.
The unearned run gave Harris a two-run cushion, and the senior right-hander responded by striking out pinch hitter Ben Jones, centerfielder Bruce Edwards and second baseman Tyler Johnstone to end the game.
Crawford took the loss as he surrendered four runs – three earned – on six hits in six innings with two walks and three strikeouts
Auburn grabbed a 2-0 lead in the first inning on an two-RBI bloop single by right fielder Russell Dixon, and LSU responded with a run in the second when right fielder Quinn Stewart singled and later scored when third baseman Mike Bianucci misplayed Jordan Mayer's sharp grounder.
Mayer gave LSU a 3-2 lead in the third with a two-out, two-run double after consecutive singles by Stewart and Liuzza.
Auburn tied the game in the bottom of the third when left fielder Luke Greinke walked and scored on Bianucci's double.
LSU wins series with 5-3 victory
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