BOSTON — The sample size grows.

And with it, the need for reinforcements, be they internal, external or both.

Any hopes that the Yankees’ starting-rotation funk would cease at one full turn — that their pitching, more generally, would stop bleeding like the stabbed undercover cop in “Witness” — evaporated quickly Thursday night at Fenway Park, as Masahiro Tanaka registered multiple career worsts and Austin Romine mopped up in a 19-3 drubbing the Yankees suffered at the hands of the rival Red Sox.

With less than a week to go before the July 31 trade deadline, the Yankees’ pitching is experiencing the worst-timed meltdown since Charlie Sheen’s a few years back. And no Yankee right now will boast of WINNING!

“This time through, obviously, we haven’t gotten length out of the starters,” Aaron Boone said afterward. “Just being up against it like we are in there, just trying to work through as best we can right now.”

The beatdown ended a two-game Yankees winning streak, attained via a pair of gritty, high-scoring wins over the American League Central-leading Twins. Even those who wear the most rose-colored pinstriped glasses, though, could see the cloud abutting the silver lining.

And with Tanaka allowing an astounding 12 runs and 12 hits in his 3¹/₃ innings, his second straight non-quality start, the Yankees’ starting pitchers have teamed for a ghastly 15.59 ERA, having allowed 41 earned runs and 12 homers over 23 ⅔innings pitched over their last six games. Loud and proud, everyone: Yeesh.

“It’s been each guy this time through,” Boone said. “It’s been one hiccup for every one of the guys that’s come in succession [that] makes it difficult. But we’ve just got to dig in and see where we can make little improvements and expect that the next time out, each guy will be sharper.”

Actually, this marks at least 1¹/₂ straight hiccups for Tanaka, who defeated the Rockies on July 20 with a six-inning, five-run effort. Combine Thursday’s effort with his two-thirds of an inning, six-run showing against the Sawx June 29 in London, and the right-hander has been clobbered for 18 runs in four innings over his last two rivalry starts.

“That’s something we’ve got to dive into a little closer,” Boone acknowledged.

“The stuff wasn’t bad. Pitches weren’t bad,” Tanaka said through an interpreter. “I do need to look at some [stuff].”

(Translation: Time to see if Tanaka is tipping his pitches, or if the Red Sox are stealing signs. Yawn.)

With their AL East margins over the Rays and Red Sox cut to 9 ½ and 10 games, respectively, the Yankees possess a cushion for a temporary malfunction. However, it’s very fair to wonder about the overall efficacy of this pitching corps.

The Yankees’ arms took such a beating in Minneapolis that they opted to place Brett Gardner, dealing with inflammation in his left knee, on the injured list Thursday and recalled lefty yo-yo Stephen Tarpley from Triple-A Scranton/Wilkes-Barre, giving them a 14th pitcher and leaving them with just a pair of bench players, Romine and Gio Urshela. That Boone proceeded to let Tanaka take a beating despite the abundance of pitchers, and that he turned to his current No. 1 catcher Romine (with Gary Sanchez on the injured list) for his second career mound turn after Tarpley and Luis Cessa took their turns, showed just how badly so many guys needed a breather.

In this year of the juiced baseball, it’ll take a village of pitchers to advance all the way to a parade. That means the Yankees really, really would benefit from acquiring a starting pitcher (Marcus Stroman? Robbie Ray? Noah Syndergaard or Zack Wheeler?) and a reliever (Sam Dyson? Ken Giles? Shane Greene? Will Smith?), plus see the returns of Luis Severino and Dellin Betances from the injured list — both men, sidelined all year, continued their slow climbs by throwing off flat ground on Thursday — and maybe even some assistance from youngster Deivi Garcia.

All of this constitutes a heck of an ask, a perhaps undoable task. The Yankees have come so far this year, though, persevering through so much adversity, that they must honor their own on-the-field efforts with front-office diligence. At this juncture on the calendar, this rough patch, this contained sample, can’t be shrugged off.