AUBURN, Ala. — With Auburn’s season down to its final strike, a defensive replacement saved the day.

Creede Simpson, who replaced a gimpy Trent Mummey in center, came through with a dramatic two-out, three-run homer in the top of the ninth to lift top-seeded Auburn to an improbable 11-10 win against Clemson in the NCAA regional Sunday.

The victory capped a marathon day for Auburn (43-20), which beat Southern Miss 17-8 in an elimination game earlier in the day before pulling out the nighttime theatrics.

“Championship baseball is about someone like Creede Simpson stepping up,” Auburn coach John Pawlowski said.

It sets up a winner-takes-all matchup with second-seeded Clemson (40-22) tonight at Plainsman Park at 7 p.m. ET. The winner advances to the super regional to play either Alabama or Georgia Tech.

“There will probably be a lot more people here tomorrow in the parking deck,” said Simpson, an Auburn native who grew up cheering for the Tigers. “I don’t know where we can fit more people. I’m sure they’ll find a way to get out here.”

Clemson looked like it had the game in the bag. It took control with a seven-run fifth inning that made it 8-5, then staved off one Auburn comeback when Mike Freeman hit a two-out RBI double in the seventh to make it 9-8.

After doing nothing in the eighth, Auburn quickly made two outs in the ninth. But Justin Bryant worked a walk before Justin Fradejas blooped a single to center that bounced in and out of the second baseman Freeman’s glove. It put runners at the corners and brought up Simpson.

The sophomore wouldn’t have been in the game if not for the quad injury Mummey suffered in last week’s SEC tournament. An All-SEC selection who was 5-for-9 on the day with four doubles and home run, Mummey grounded out on a nubber to third with the bases loaded to end the seventh, struggling to get down the line.

Once he got out to his position in center for the next half-inning, Pawlowski, not liking how Mummey was moving, replaced him with Simpson. When Mummey reached the dugout, he took off his glove and fired it in frustration.

“I’m not going to play somebody if I don’t think they’re 100 percent,” Pawlowski said. “Trent has given us everything he is capable of, but I had a sense at that time that he wasn’t feeling as well as he had been.”

Clemson coach Jack Leggett admitted he didn’t have much of a scouting report on Simpson, a seldom-used outfielder whose playing time diminished once Mummey returned from an ankle injury at midseason. Simpson’s only appearance in the regional prior to Sunday night was as a pinch runner in the Southern Miss game.

Leggett decided to stick with reliever Tomas Cruz (3-3), who already allowed the tying runs to score two inning prior.

Cruz got ahead in the count 1-2 when Simpson crushed his fourth pitch, a waist-high hanger on the inside corner, over the big wall in left.

“He had been throwing some pretty good sliders,” Leggett said. “That one didn’t do much.”

“I was trying to get the barrel on the ball,” Simpson said. “I knew I had a great opportunity. I didn’t want to waste it.”

Simpson sailed around the bases, mobbed by his teammates once he reached home.

“When the fans were on their feet screaming, it was the loudest I’ve ever heard that stadium,” Pawlowski said.

Prior to Sunday, Auburn was 0-16 when trailing after eight innings.

Reliever Austin Hubbard (6-2) pitched through a nerve-racking ninth to close things out, allowing a run and putting runners at the corners before getting Jeff Schaus to pop out to end things.

“Austin Hubbard, I’ve said it before, he’s the guy you want out there in big situations,” Pawlowski said.

Hubbard, Auburn’s closer, threw 76 pitches in 4 2/3 innings, allowing five runs (three earned) on eight hits.

“That is my baseball highlight,” the senior said. “The crowd, Creede’s home run, the way we battled. And I hope I get to make another highlight tomorrow night.”