UC Santa Barbara first baseman Cole Mueller was suffering from a stomach ailment at the start of Friday’s Big West baseball game. Three hours, 18 minutes later, it was Hawaii feeling the pain.

Mueller’s walk-off RBI single completed a two-run ninth and rallied the Gauchos to a 6-5 victory at Caesar Uyesaka Stadium in Santa Barbara, Calif.

“I’m feeling good now,” Mueller told BigWest.tv after the game. “It was nice to get that hit at the end.”

Mueller’s hit was against closer Dylan Thomas, who struggled in an 11-batter appearance, and overshadowed Dustin Demeter’s dramatic homer for UH in the top of the ninth.

“You’re always disappointed when you get left on the field like that, especially when you’ve got your stud closer on the mound,” UH coach Mike Trapasso said in a telephone interview. “He didn’t have it. You can’t get upset with that guy. He’s been amazing all year.”

The Rainbow Warriors ousted UCSB starter Chris Lincoln, who exited in the third with a 4-1 deficit. But the ’Bows could not solve left-handed reliever Ben Brecht, who retired 16 of the first 18 batters he faced.

“That guy was carving us up,” Trapasso said of Brecht. “He was unbelievable. We were making him look like Clayton Kershaw out there. As good as he was throwing, we had no chance for six innings.”

But with the score tied at 4 in the top of the ninth, Demeter stepped into the batter’s box — and stayed there. On the 18th pitch of the at-bat, Demeter pulled a drive over the fence in right field. Demeter was hitting .118 against left-handed pitchers prior to that homer.

“It was the best at-bat I have ever seen at the college level,” Trapasso said. “And it’s a shame we weren’t able to close it out so it could be a game-winner.”

Thomas worked out of a bases-loaded jam in the seventh inning, but surrendered a run in the eighth. In the ninth, Thomas surrendered a one-out single to Tommy Jew. Thomas Rowan then hit a drive to left-center that fell for a double. Center fielder Dylan Vchulek thought left fielder Johnny Weeks had called for the ball; Weeks had not. Vchulek might have been confused by fans who were yelling from behind the fence.

“Whatever,” Trapasso said. “That’s a ball we’ve got to catch.”

Pinch hitter Sam Cohen then hit a sacrifice fly to right to score Jew to tie it at 5-all.

Mueller was instructed to hunt for the slider, Thomas’ out pitch. The first pitch sliced inside to the right-swinging Mueller. Mueller drove the second pitch — also a slider — to the gap in right center to trigger a wild celebration.

“I sold out trying to win this one by bringing in Dylan in the seventh,” Trapasso said. “Unfortunately, it was the first time all year he didn’t have it. That’s all she wrote. He didn’t have anything. I considered taking him out. He kept teasing he might be able to find it. It’s unfortunate it came on his last outing of the year. But the guy has been amazing for us all year. The law of averages catches up to everyone eventually.”

Thomas entered with a 1.22 earned-run average and two walks in 37 innings. In two innings on Friday, Thomas allowed four hits, two walks and three earned runs.

The ’Bows dropped to 26-24 overall and 10-13 in the Big West. The Gauchos are 27-27 and 10-13.

The teams meet today at 11 a.m. in the regular-season finale.