Clay Holmes isn’t supposed to walk off the mound mid-inning.

But the Yankees’ closer found himself doing just that in the ninth inning Tuesday night. In a rare occurrence in this otherwise brilliant season, Holmes proved mortal, failing to record an out and sparking a stunning Reds comeback.

Twenty-four hours later, Holmes toed the Yankee Stadium rubber again, pitching the ninth inning in a tie game.

Though he was not quite his impeccable self, Holmes nursed his way through a 23-pitch scoreless inning, stranding a pair of baserunners and setting the stage for the Bombers’ 7-6, 10-inning victory Wednesday night over the Reds.

“Last couple of nights have been a grind for him,” manager Aaron Boone said. “He figured it out, grinded his way through it, made some big pitches and got us back in the dugout.”

On Wednesday afternoon, Holmes expressed an eagerness to return to the mound.

“There’s a full confidence to put this one behind me and move onto the next one,” he told The Post. “I just want to go out there and put a clean inning up.”

Clean innings have been the norm for Holmes, who has allowed an earned run in just three of his 40 appearances this season.

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Holmes watched film of his outing Tuesday, alongside pitching coach Matt Blake. The pair identified slight posture and mechanical issues, and Holmes called the tweaks “minor.”

For closers, physical adjustments are only half the battle. There’s a mental struggle, too. While one blown save does not warrant panic, it marked Holmes’ first true meltdown since he seized the closer’s spot in May.

“The closer’s role, there is some responsibility with that,” Holmes said. “But at the same time, you give up runs, it’s never what you want. You just have to try and learn from it and move on.”

Wednesday night, Holmes did just that, though he was by no means perfect.

He issued a leadoff walk to the No. 9 hitter, Stuart Fairchild, and fell behind the next hitter, Jonathan India, prompting what Holmes called a “light-hearted” mound visit from first baseman Anthony Rizzo.

Holmes wriggled out of trouble. With two on and one out, he fell behind Tommy Pham, 3-0. But Holmes escaped, inducing a lazy fly out by Pham and a ground out by Joey Votto.

“It’s something I wasn’t able to do [Tuesday],” Holmes said. “It wasn’t quite there [Wednesday], especially early on. As the inning went on, I started to get that feel back.”

This wasn’t Holmes at his sharpest — if it had been, Lucas Luetge would not have been summoned to warm up, and the Yankee Stadium crowd would not have moaned and groaned.

But this was Holmes, unlike Tuesday, still good enough.