Yankees starting pitcher Gerrit Cole pitches during the first inning of...

Yankees starting pitcher Gerrit Cole pitches during the first inning of Game 1 of a doubleheader against the Guardians at Progressive Field on Saturday in Cleveland. Credit: Getty Images/Nick Cammett

Let’s finally put to rest any debate involving Gerrit Cole’s status as the ace of the Yankees’ rotation. Not only is he looking like the last one remaining in the deck, but this once-dominant group has looked more ordinary lately, and it’s about to be reshuffled.

Before Cole took the mound Tuesday night against the lowly Reds, the Yankees’ starters -- a strength over the first half -- were a combined 6-6 with a 4.79 ERA in 21 starts since June 19 (the team’s record was 12-9). That ERA ranked 23rd in the majors over that span -- sandwiched between the Royals and Reds -- and some of the other stats had slipped as well, as they ranked 10th in both K/BB ratio (3.35) and WHIP (1.18).

Being in MLB’s top third in those categories is certainly respectable. The shocking part, at least in the midst of this Yankees’ historic season, is the noticeable dip over this recent stretch. Along with the looming concerns regarding the red-lining number of innings for both Nestor Cortes and Luis Severino.

Up to the aforementioned cutoff point, the Yankees had mowed through the league, in part due to Cortes polishing his All-Star credentials (and building a Cy Young case). They were 28-6 through the first 65 games, with a 2.71 ERA that ranked second in the majors behind the Dodgers (2.58). The Yankees also were first in WHIP (1.01) and K/BB ratio (4.91) as well as second in opponents batting average (.215).

But that momentum has shifted since everyone started arguing over who should be the Yankees’ Game 1 starter come October. The challenge now for Aaron Boone & Co. is to make sure a few of the current rotation members are still standing by then. Despite Cole getting knocked around up at Fenway over the weekend -- specifically by his personal nemesis Rafael Devers -- he remains the $324-million ace the Yankees have to lean on. It boils down to season-long stamina, which is in dwindling supply for some in this rotation.

Take Cortes. He’s been an incredible story this first half, fulfilling Boone’s spring-training prophecy of not only making the rotation, but earning an All-Star invite to L.A., just as the manager told him in Tampa. But there’s a more worrisome reality at play for the second half, all because of his innings total so far.

In that sense, Cortes has become a prisoner of his own breakout performance. After throwing a career-high 93 innings last season, Cortes is already at 88 2/3 through his first 16 starts. According to pitching coach Matt Blake, the general rule of thumb is a 30% bump from one year to the next, and that would put Cortes on a limit of approximately 121 innings for this season. At this current pace, that would only give him another six or seven starts, so the Yankees need to start getting creative to preserve him.

“It’s certainly something we’re paying attention to closely,” Boone said before Tuesday’s game. “If at any point we have to skip or do whatever we have to do, we’ll do that.”

Severino is an even more extreme case than Cortes, having thrown just six innings last season coming off Tommy John surgery -- so he’s already blown through his projected limit at 84 through his first 15 starts. But while it’s sensible to set boundaries in theory, putting the brakes on two of the Yankees’ best starters is not something anyone wants to do -- Boone, Blake or the two pitchers themselves.

Cortes, at age 27, has worked extremely hard -- through three different MLB stops -- for a dream season like this one. Severino, now 28, finally has straightened out a career repeatedly derailed by injuries. Nevermind the fact the Yankees need both for a shot at a 28th World Series title.

Fortunately, being 36 games over .500 (61-25) with a 14 1/2-game lead in the AL East should give them the luxury to protect Cortes and Severino without sweating the division. The Yankees have been strategizing for this day for a while.

“Everything is on the table,” Blake said.

And what is defined by everything? Severino already was moved to Wednesday, preventing him from making two starts before the All-Star break, and he’ll join Cortes at the back end of the rotation when the Yankees kick off the second half.

But that’s only the beginning. A six-man rotation remains a possibility at some point, and in any case, expect to see less of Cortes and Severino after the break. The Yankees are likely to piggyback their starts with other stretched-out arms like Domingo German, Clarke Schmidt and JP Sears to preserve innings. The Yankees also are checking out the prices on available starters before the Aug. 2 deadline, mindful of these rotation concerns as they eye a long October run. Here in mid-July, they still need the gas to fuel it.

“We’ll continue to try and be as vigilant as we can,” Boone said.

Riding Cole has never been more crucial as they figure out the rest.

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