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LSU starting pitcher Landon Marceaux (11) takes the mound to pitch against Auburn, Friday, May 17, 2018, at LSU's Alex Box Stadium in Baton Rouge, La.

In the fourth inning Friday night, freshman Landon Marceaux jogged to the bullpen down the right-field line. He threw in foul territory, waiting to pitch again.

On the field, LSU batted around, scoring four runs to give Marceaux the lead. As the inning continued, Marceaux kept his arm loose. He had retired 11 straight batters and allowed one hit, which he erased with a double play.

As Marceaux completed the best start of his young career, LSU beat Auburn 5-1 at Alex Box Stadium. When Ole Miss lost a few minutes later, LSU clinched the No. 5 seed in the Southeastern Conference tournament. The Tigers will play at approximately 8 p.m. Tuesday against the No. 12 seed.

LSU (34-21, 17-12) won its fourth straight game and clinched the series.

"The most thrilling thing, maybe in a long time," coach Paul Mainieri said, "was the effort of Landon Marceaux."

Against Auburn (31-23, 13-16), Marceaux showed ability LSU had seen since he arrived on campus last fall, ability derailed by a mid-season injury.

LSU put Marceaux in its weekend rotation. He had not allowed a run during preseason practice. Marceaux struggled in his third start, then he felt a pinch in his shoulder. The pain stunted his development as he pitched twice over the next six weeks.

As Marceaux struggled to get healthy, his confidence dropped. His injury led to frustration. Just like the rest of the team, Marceaux had expected himself to play well this season.

"You always knew it was in there," junior pitcher Zack Hess said. "It wasn't a matter of if he was going to succeed here. It was just a matter of when."

Marceaux pitched well once he regained his health, but never like this. With command of all three pitches, Marceaux lasted a career-high seven innings. He struck out a career-high seven batters. He retired the side five times.

Marceaux did not allow a run until the fifth inning, when he gave up a solo home run to center field. He retired the next nine hitters, conserving LSU’s bullpen for the final game of the regular season Saturday.

If Marceaux had stayed healthy this season, Mainieri said he thought he would have pitched like that multiple times already.

While Marceaux cut through Auburn’s lineup, LSU’s hitters supplied run support in the fourth inning.

With the bases loaded and one out, Auburn pitcher Jack Owen hit Beloso, bringing in the game’s first run. A wild pitch let another run score. Then, with two outs, catcher Saul Garza reached on an infield single as LSU scored again.

Josh Smith soon hit a line drive off the glove of Auburn shortstop Will Holland, a single that gave LSU a 4-0 lead.

Marceaux didn't need anything else. After seven innings, Mainieri took him out because he will pitch on short rest next Thursday if LSU advances that far in the conference tournament.

"There was a lot of hype around him," said Hess, who pitched two shutout innings, "and I think everyone is starting to see why."

LSU has played complete games the past two days, wining on timely hitting and the strength of its pitching. It has held Auburn to four hits during the series. The Tigers feel confident as the postseason approaches.

But as LSU's players stood in right field, Mainieri told the team about the importance of Saturday's game. The Tigers know their SEC tournament seed. Now they need as many wins as possible to earn consideration for hosting an NCAA regional.

"It's senior day, and we're going to have some juniors (leave after this season), and if we don't host a regional, this will be their last game in the Box," Mainieri said. "We need to send them out the right way."

Follow Wilson Alexander on Twitter, @whalexander_.