LSU had a series win in its grasp.

Then, suddenly, it was gone.

Texas A&M erased a three-run deficit in the ninth inning of a Saturday afternoon stunner at Alex Box Stadium, scoring four runs in the ninth inning against LSU closer Caleb Gilbert.

The big lick was a two-out, three-run homer by Walker Pennington that gave the Aggies a 4-3 win.

“It’s about as tough a loss as we could have. ... We were one out away from winning a series against a good team,” coach Paul Mainieri said.

LSU (19-10, 5-4 Southeastern Conference) looked like it had a comfortable lead going into the ninth. The combination of freshman Eric Walker and senior Hunter Newman had allowed just five base runners and no runs in the first eight innings.

But things clicked for Texas A&M (19-10, 3-6) against Gilbert. Three of the Aggies’ seven hits came in the ninth, and Pennington’s blast was the decisive blow. Pennington entered the game as a defensive replacement in the seventh inning.

“His home runs tend to matter for us,” Texas A&M coach Rob Childress said.

This one certainly did.

Gilbert fell behind in the count and tried to sneak a fastball over the outer part of the plate. The pitch leaked back out over the heart, and Pennington blasted it over the wall in left field.

It was the first blown save for Gilbert this season. He was successful in his three save opportunities while Newman was recovering from a back injury.

“I let the team down today. Didn’t make the pitches when I needed to,” Gilbert said. “I didn’t have the command that I would’ve liked to have, especially with my secondary pitches. It put me in a hole, they put some good swings on some balls and it happened.”

Mainieri did not consider leaving Newman, fresh off a back injury that kept him sidelined for two weeks, in for the ninth inning.

“He’s got a bad back. It’s amazing he even pitched at all,” Mainieri said. “He was out of gas two days in a row, it was unbelievable he could even throw. He couldn’t pitch any more. Physically, he was not capable of it.”

LSU brought the middle of the lineup to the plate in the bottom of the ninth inning, but the Tigers went down in order. Their last chance was snuffed out when Aggies center fielder Nick Choruby made a difficult catch in the left-center gap to rob Josh Smith of extra bases.

LSU and Texas A&M had trouble figuring out each other's starting pitchers, both of whom turned in the longest outings of their careers.

Walker — who didn’t make it out of the fifth inning in his start against Florida last week — threw seven marvelous innings Saturday, striking out seven and walking just one. Walker retired 16 of the final 17 batters he faced. That string started when he loaded the bases with two outs in the second but blew a 3-2 fastball past Choruby to get out of danger.

“He did a lot of great things out there,” Mainieri said. “He pitched very courageously.”

Texas A&M right-hander Corbin Martin was almost as good. The converted reliever was making his fifth career start and had never lasted more than five innings, but he tossed eight innings Saturday and held LSU to a season low in hits (four).

“He’s starting to transform from a thrower to a pitcher and growing in that respect. ... He had a great one today,” Childress said.

LSU shortstop Kramer Robertson broke a scoreless tie in the fourth inning when he turned on a high fastball from Martin and sent it soaring over the wall in left for a two-run homer. It was Robertson’s third home run of the season and second in two days.

The Tigers pushed their lead to 3-0 in the next inning when Zach Watson singled past a drawn-in infield to score Beau Jordan from third base.

LSU will host Grambling at 6:30 p.m. Tuesday.

Follow Luke Johnson on Twitter, @ByLukeJohnson.