A day after some stellar defense helped the Yankees secure a 1-0 win over the Red Sox, sloppy play doomed the pinstripers in a 6-0 loss that kicked off a doubleheader against Boston.

The fifth frame of the rivals’ Saturday afternoon matchup was particularly tough on the Bombers, as second baseman Amed Rosario threw a ball away in an attempt to double off Adley Rutschman at first after catching a line drive for the second out of the inning. The low misfire from Rosario — always a liability on defense but in a less-than-inspiring, righty-heavy lineup against the left-handed Jake Bennett — gave the Red Sox a runner in scoring position before an infield single.

Ali Sánchez, who has cost the Yankees his fair share of runs despite minimal playing time, was then charged with a passed ball behind the plate. That allowed Rutschman to score Boston’s second run of the game.

Wilyer Abreu gave the Sox their first run when he homered off Carlos Rodón in the opening inning. Rodón, now three starts removed from an IL stint for elbow inflammation, totaled two earned runs, three hits, one walk and five strikeouts over 4.2 innings and 88 pitches.

It was less length than the Yankees would have liked with Max Fried, returning from the IL after his second left elbow bone bruise of the season, starting Game 2 of the doubleheader. However, Rodón wasn’t helped by Rosario or Sánchez.

Rosario was also thrown out at home plate in the fourth inning after Red Sox center fielder Ceddanne Rafaela got turned around and couldn’t catch a Heliot Ramos flyball.

Initially holding and retreating back toward second base in case he had to tag up, Rosario did not get a good jump as Rafaela whiffed on the catch and the ball bounced to the wall in center. Still, Yankees third base coach Luis Rojas waved Rosario home, a brutal mistake.

Rosario had just rounded third when Sox second baseman Nick Sogard caught the relay throw from Rafaela. Sogard threw Rosario out by several feet, prompting a discussion between Boone and Rojas after the inning.

Boston, meanwhile, scored four more runs in the ninth. That ugly inning saw a shallow flyball drop between George Lombard Jr., Jazz Chisholm Jr. and Trent Grisham. Cody Bellinger also slipped on a play, helping the Red Sox score another run, and Ryan Yarbrough threw a wild pitch while getting knocked around.

With the Yankees unable to score off Bennett or any other BoSox pitcher in Game 1, their lead over Boston for the American League’s top wild card spot fell to two games.