CLEARWATER, Fla. — Luis Severino will start the season as the Yankees’ fourth starter.

How long he stays in the job, Joe Girardi said Thursday, is up to the talented but up-and-down righthander.

“He needs to take this and run with it,” Girardi said of the 23-year-old, who has continually frustrated the Yankees with his inconsistent fastball command.

Though Girardi said he doesn’t want Severino “looking over his shoulder,” he added: “This is a performance-based business, so you have to perform.”

Severino, who allowed one run and five hits in five innings in his final exhibition start Thursday against the Phillies — a 14-1 victory that put the Yankees at an MLB-best 24-8 — said he understands the warning.

“It feels very good. I’m happy they’re giving me a chance to be a starter,” Severino said. “I have to be that starter that they [think] I am.”

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Lefthander Jordan Montgomery and righties Chad Green and Luis Cessa will compete for the fifth spot during the first two weeks of the minor-league season. Because of several off days early in the season, the Yankees don’t need a fifth starter until April 16. Green will pitch for Double-A Trenton and Montgomery and Cessa will pitch for Triple-A Scranton/Wilkes-Barre.

Severino, who won a rotation spot in spring training last year but lost it after falling to 0-6 with a 7.46 ERA on May 13, was told Wednesday that he had secured the fourth starter job.

After the Yankees spotted him a 9-0 lead in the top of the first inning Thursday, Severino struggled, allowing a run on a walk and two hits.

But he was perfect in the next three innings before leftfielder Clint Frazier’s misplay leading off the fifth led to a double. Severino, who walked one and struck out four in lowering his ERA to 3.38, got out of the inning anyway.

“After the first inning, I thought he was pretty good,” Girardi said. “Step in the right direction.”

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In addition to tabbing Severino as the fourth starter and making official his position players for Opening Day — Ronald Torreyes will be the starting shortstop and Pete Kozma the reserve infielder — Girardi announced his bullpen to start the year.

With the Yankees not needing a fifth starter yet, they’ll leave camp with eight relievers: Aroldis Chapman, Dellin Betances, Tyler Clippard, Tommy Layne, Adam Warren, Bryan Mitchell, Jonathan Holder and Chasen Shreve. Warren and Mitchell will be the long men.

“We don’t have a rotation that you expect they’re going to give you seventh, eighth inning every time they go out,” Girardi said. “So you’re going to need some distance [from some relievers].”