BOSTON — Even if Brian Cashman registers the best week of his long career, he still won’t land the Yankees five new starting pitchers by Wednesday’s trade deadline.

Therefore, if they want to get to where they desire to go, a few guys currently working in the Yankees’ rotation must wake up and deliver. And no slumber is hurting the American League East leaders as much, arguably, as that of the new guy, James Paxton.

The Big Maple got pummeled again Friday night, his Fenway Park debut as a Yankee going about as well as Jackie Mason’s debut as a sitcom star. By getting knocked around for seven runs and four homers — three by reigning AL Most Valuable Player Mookie Betts — in only four innings, Paxton wore his club’s 10-5 loss to the rival Red Sox, its second straight, and extended a hellacious run of Yankees starting pitching to an unlucky seven games.

“I wanted to be able to give us some length tonight,” Paxton said. “Unfortunately, I didn’t do that. So hopefully we can get this thing turned around starting [Saturday].

About “this thing,” ready for the ghastly numbers? In their past seven outings, the Yankees’ starters have combined to allow 48 earned runs in 27²/₃ innings pitched, a 15.61 ERA and 16 homers. Say it once, say it twice, say it three times if you must: Yeesh.

“Certainly, obviously, we can’t deny that we hit a bad stretch here,” Cashman said Friday — before the game.

Paxton ranked as Cashman’s big get last winter, procured from the Mariners for top pitching prospect Justus Sheffield (who also has underwhelmed, alleviating the Paxton pain) and two other minor leaguers, and early on, he seemed to be a hit. Most notably, he dominated the Red Sox the first time he faced them as a Yankee, allowing two hits and a walk while striking out 12 over eight innings on April 16 in The Bronx, and he followed that with two more solid starts before exiting his May 3 start with a left knee condition that sidelined him for nearly a month.

Since his return, the 30-year-old has been, well, inconsistent. If not terrible, then certainly not frontline. After absorbing this Back Bay beating, his ERA stands at an ugly 4.72.

It gets ugly early in these Paxton outings. Amazingly, when Betts started the bottom of the first with a blast over the Green Monster, Paxton notched his third straight start in which he had surrendered a leadoff homer. Rafael Devers followed with a base hit and, one out later, J.D. Martinez crushed a two-run homer to left-center field. Paxton’s 11.00 first-inning ERA ranks as the worst among all pitchers who have recorded 10 or more starts, per YES Network statistician James Smyth.

“It’s just about getting amped up for the first inning. Try to bring my best out right from the start,” Paxton said. “I felt like I did a pretty good job of that tonight, but same thing. Gave up some tough hits, missed a couple of spots and gave up some home runs, unfortunately.”

“I thought stuff-wise, I thought he was electric,” Aaron Boone said of Paxton, citing his impressive ratio of nine strikeouts to no walks.

The Yankees’ manager added: “To get every mistake really hit for slug hurt him and cost him. So yeah, it’s frustrating when you out there with, I thought, really good stuff.”

If the Yankees’ most important pitching acquisition of last offseason doesn’t find higher ground soon, he’ll be drawing comparisons to his New York-phobic predecessor Sonny Gray. And because Paxton has disappointed, Cashman must work harder to find more arm reinforcements and hope they don’t turn into Sonny Sequels.

The Yankees’ AL East lead remains a robust 8 ½ games over the Rays and nine over the Red Sox. No reason to draw that any closer, though, right? Who will lift the Yankees out of their pitching funk?

Paxton has as good a chance as anyone currently here. If he honors his ceiling, harnesses his obvious high-end stuff, boy oh boy will he increase the Yankees’ chances of finishing great — and, in the process, decrease Cashman’s blood pressure.