Asked Saturday morning about how he planned to complete 18 innings of a doubleheader with a pair of starting pitchers who were not fully built up from injuries, manager Aaron Boone raised both arms with upturned palms: a shrug.

The concerns around the club then only grew as play began.

The Yankees made mistake after mistake, including an error and a passed ball combining to let in a fifth-inning run and cost Carlos Rodón needed length. An ugly ninth inning featured Cody Bellinger slipping to let in another run and the Red Sox teeing off against Ryan Yarbrough.

There also was a questionable green light from third base coach Luis Rojas, which resulted in the best offensive chance of the club’s afternoon being neutered.

But such concerns with the pitching, defense and decision-making became secondary.

Sure, the Yankees did not play a perfect game, but they were most imperfect when they were on the attack.

The Yankees again were quiet against a Red Sox lefty, this time Jake Bennett, in what became a 6-0 loss in front of a sellout crowd of 47,314 on a sunny Saturday afternoon in the start of a long day of significant baseball in The Bronx.  

Before the nightcap, the Yankees (76-59) had alternated wins and losses in their previous eight games and temporarily fell to two games ahead of the surging Red Sox (74-61) for the top wild-card spot and 4 ½ games behind the Rays in the division.

For probably its biggest series of the season, Boston stacked its lefty pitchers — Patrick Sandoval on Friday, Bennett on Saturday afternoon, likely a lefty opener in the nightcap and Ranger Suarez on Sunday — to exploit a potential Yankees weakness that sure has looked like a real weakness so far.

In the first two games, the Yankees scored one run — the difference-making home run from Paul Goldschmidt a night earlier — on seven hits and 20 strikeouts. Of those seven hits, all were scattered: The Yankees had not logged multiple hits in any frame.

Without Aaron Judge and Giancarlo Stanton, Boone turned to righties such as Goldschmidt (0-for-4), Amed Rosario (0-for-4) and Heliot Ramos (1-for-2). Some of the Yankees’ best bats, such as Luis García Jr., Trent Grisham and even the reasonably hot Jazz Chisholm Jr. and Austin Wells, came off the bench.

It did not help that the Yankees ran themselves out of their best opportunity against Bennett.

In the fourth, the Yankees got a rare base runner when Rosario reached on a one-out error and then took second on a passed ball.

Ramos then stepped into a Bennett fastball, doubling to center over a turned-around Ceddanne Rafaela. Rosario was tagging up on the play, did not take off until it hit dirt, then did not stop as Rojas’ windmill kept blowing him home. The Red Sox’s relay — Rafaela to Nick Sogard to Adley Rutschman — was perfect, nailing Rosario by a few steps for the second out of the inning.

Bellinger, who would have been up with one out and runners on second and third if Rojas had put up a stop sign, then struck out.

The Yankees did not reach second base again. Their other decent threat, in the fourth inning, involved José Caballero reaching scoring position on a single and an error before Spencer Jones and Ali Sanchez struck out and Goldschmidt popped out.

Four runs on four hits and two walks against an exhausted Yarbrough in the ninth — aided by Bellinger’s slip bringing home Andruw Monasterio — turned a two-run game into a rout.

The Red Sox only scored off Rodón (4 ⅔ innings, two runs) with a first-inning home run from Wilyer Abreu and a chaotic fifth inning.

With one out and Rutschman on first, Monasterio lined directly to Rosario at second base. Rosario caught it and tried to double up Rutschman at first, but he bounced the throw, which hit Rutschman and ricocheted into foul territory to move the catcher to second.

Sogard then hit a hard ground ball down the third base line, where José Caballero did well to chase it down with a sliding backhand, but then bounced an off-line throw to Goldschmidt for an infield single.

Instead of four outs, the Red Sox only had two, which mattered when Rodón’s slider ticked off Sanchez’s mitt and to the backstop. Rodón and Rutschman both barreled to the plate, and Rutschman won the race.

Rodón then walked Eli White and drilled Jahmai Jones, pulled from a game in which his stuff was excellent but his defense less so.