BOSTON — After more than a five-hour delay due to a mechanical issue on their charter, the Boston Red Sox did not arrive from Denver until 5 a.m. Thursday. Of all days to have plane troubles and not much rest, the Red Sox were to face the American League Cy Young favorite, Cam Schlittler, later that day.But by the time Thursday’s game had ended, it was the New York Yankees who looked sluggish. The Yankees lost 6-3 in their ugliest game of the season. None of the runs the Red Sox scored were earned. It was the most unearned runs the Yankees have allowed in a game while holding their opponent out of the earned-run column since July 21, 1913, according to Stathead. The world’s oldest living person, according to Guinness World Records, was just 3 when the Yankees played such a game.“We just didn’t do a good job of taking care of the ball,” Yankees manager Aaron Boone said. “Just not up to the way we’ve been playing, or capable of playing. Ultimately, it was too much to overcome.”The Yankees committed four errors. Austin Wells was called for catcher’s interference in the first inning. Schlittler had an errant pickoff attempt in the same inning. Amed Rosario watched a ball go between his legs at third base in the fifth. And Yerry De los Santos could not field a sacrifice bunt in the eighth.Rosario’s error was the costliest play of the game. With runners on first and second and one out, Red Sox first baseman Willson Contreras hit a 112.8 mph rocket at Rosario. If the third baseman had fielded the ball cleanly, the Yankees would have escaped the inning with a double play and still led 2-0. Instead, the ball zoomed between his legs and rolled to the wall, scoring one.“Definitely a play there that I just got to make,” Rosario said through Yankees interpreter Marlon Abreu. “I take responsibility there. When you look at the play, you at least have to find a way to knock it down and get one out.”Jarren Duran followed with a tying sacrifice fly to shallow left field. Technically, there wasn’t an error, but José Caballero’s throw home was poor. He fired it to the plate at 90.2 mph, but it was well off line. A better throw, and Caballero nails Ceddanne Rafaela with ease.“They know I’m kind of new in the outfield, so they’ve been challenging me,” Caballero said. “I was expecting him to go.”The Yankees’ outfield alignment since Trent Grisham injured his hamstring has been an adventure. Caballero entered Thursday’s game with just 72 career innings in left field, while Jasson Domínguez, a below-average outfielder anywhere he plays, played the other corner. Boone said pregame he wanted Domínguez in right field, which is considerably more challenging at Fenway Park due to its spaciousness, because of his speed to cover potential balls hit in the gaps.Boston started left-hander Connelly Early, which meant left-handed-hitting outfielder Spencer Jones was on the bench. Boone has not shown a willingness to play Jones against lefty pitchers who do not have reverse splits. That means, effectively, Jones is a platoon bat right now. For the time being, he will make nearly all of his starts only against right-handers or lefties who are ineffective against left-handed hitters.Cam Schlittler allowed four runs — his second most in a game this season — but his ERA dropped to 1.62. (David Butler II / Imagn Images)While it’s impossible to know how things would have played out, Jones’ ability to handle left-handed pitching could have given the Yankees the flexibility to start Caballero at third base, Jones in center field and Cody Bellinger in left field Thursday. Instead, their worst defensive alignment cost them a win.Boone said he considered starting Rosario in left field and Caballero at third base for Thursday’s game but opted not to because Schlittler doesn’t usually allow pull-side results. Entering his start Thursday, 22.1 percent of at-bats against Schlittler ended with a groundball to the pull side, according to Statcast. But there is a higher likelihood of an at-bat ending with a pull-side groundball than a pull-side fly ball, which had happened only 11.7 percent of the time this season. If Boone was playing the percentages, it was likelier for the ball to find the third baseman than the left fielder with Schlittler on the mound.“Rosie is capable of making all those plays,” Boone said. “He didn’t make a play on a ball that, in fairness, was absolutely lathered. Contreras pummeled that ball. We don’t make a play there. That’s going to happen. When you have a handful of situations where you’ve got a chance to make the play, you’ve got to make them, especially in a close game.”Other sloppy plays from the Yankees did not register as errors. Schlittler and Wells allowed a popup to fall between them for an infield single. Anthony Volpe could not turn a tailor-made double play in the eighth, which allowed a run to score.It was an ugly all-around defensive game for the Yankees, who have not graded out well statistically this season. In defensive runs saved, the Yankees were tied for 21st and tied for 15th in outs above average entering Thursday.But the Yankees had not been historically bad, which they were against the Red Sox in the first of a four-game series.“It’s not fun going through that or fun when you make mistakes in a game, especially one that you have a lead,” Boone said.