DETROIT — Throughout spring training, CC Sabathia hardly acknowledged that he was in a competition for a rotation job.

He felt good physically when he reported to Tampa on Feb. 18, he said, and felt just as good when the exhibition season ended.

That the Yankees waited until the very last instant to name him the winner of the competition against Ivan Nova was of little consequence, as were his poor spring numbers. Sabathia’s expectation all along was that he’d be the fifth starter.

He was, he kept saying, “ready to go” for the regular season. And in arctic conditions Saturday afternoon against a lineup that didn’t look like a good matchup at all, he showed he was just that.

Mostly keeping the righthanded-hitting Tigers off balance, Sabathia became the first Yankees pitcher of the season to last at least six innings, paving the way for an 8-4 victory in front of 32,419 fans at Comerica Park who were bundled in layers against the 31-degree first-pitch temperature.

“It’s a guy you can count on, and he’s been that guy the minute he got into the big leagues,” Brian McCann said. “He’s carried staffs his whole career and now he was asked to be the fifth starter and he’s taken it in stride. He’s a big-time competitor. Love to have him on the mound. He can win a lot of games in this league still.”

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The 35-year-old lefthander, perfect through three innings, was charged with three runs and allowed four hits and four walks in six innings-plus. Sabathia left with the score 8-2 and Jose Iglesias on first after a single, and he later scored on a wild pitch by Kirby Yates.

Sabathia was aided by an offense that drove former Met Mike Pelfrey (six runs, eight hits) from the game after 3 2⁄3 innings and collected 14 hits overall, including a three-run triple by Jacoby Ellsbury, a two-run homer by Carlos Beltran and a solo shot by Alex Rodriguez.

“I mean, all spring I felt good, I didn’t have any problems,” said Sabathia, who had a 5.51 exhibition ERA. “Mechanically I felt good, my knee was feeling good. I just felt like I was trying to get my work in, and get to here and have my pitches make the action they’re supposed to. It was good.”

The outing was of particular importance to the Yankees’ bullpen, taxed the first four games as no starter lasted longer than 5 2⁄3 innings.

“It’s really good, and on a day where we needed some innings,” Joe Girardi said. “To do it against a lineup that really has big righthanded bats, I thought that was impressive today . . . He gave us a big start today.”

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Three veteran Yankees who received days off the day before — causing a bit of criticism to be directed Girardi’s way — had big afternoons. Rodriguez hit his first homer of the season with two outs in the first inning, Beltran went 2-for-4 with his second homer and McCann went 2-for-4 with a walk and scored three runs.

Ronald Torreyes, who won a utility infield job in spring training and started for Chase Headley at third, went 3-for-4. Didi Gregorius drove in two runs and Ellsbury’s bases-loaded triple with two outs in the fourth gave the Yankees a 6-0 lead and knocked out Pelfrey.

“You’re getting production up and down the lineup,” Girardi said. “It seems to be a different person every day. That makes your lineup really deep and hard to navigate.”

But Sabathia’s efforts stood out most of all, particularly in the clubhouse, where no one is more respected than he is. And his standing only grew after he admitted himself to alcohol rehab last October.

“I love CC,” A-Rod said. “Everyone in this clubhouse has tremendous appreciation for CC.”

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Included in the large group of family watching Sabathia in person were his wife and mother, the two people with whom he was most looking forward to sharing that afternoon’s success.

“They were there every step of the way,” Sabathia said. “Obviously, these guys in here were great, but my mom and my wife were that rock for me in that tough time. So it will be good to see them tonight.”