NEW YORK -- When it comes to the Red Sox’s postseason chances, momentum has become an even bigger problem than math.

Hoping to build off an emotionally charged victory on Saturday against their rivals, the Red Sox instead slipped right back in a 5-2 defeat at Yankee Stadium on Sunday to cap a series in which New York took three of four on its home turf.

While the Yankees are almost certainly going to the playoffs, Boston (75-75) is hanging by a thread, trailing the Twins by 4 1/2 games for the third American League Wild Card spot with 12 games left. The Tigers and Mariners also remain ahead of the Red Sox.

“We’re 4 1/2 games back and Detroit [and Minnesota] won, and it’s getting tougher and tougher,” acknowledged Red Sox manager Alex Cora.

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Only Minnesota’s struggles of late have kept Boston that close. And the fact that the Twins are coming to Fenway for a three-game series on Friday gave the Red Sox some hope in recent days.

The problem is that the Red Sox have been unable to get on any kind of a run down the stretch. Boston’s three-game winning streak from Aug. 4-6 is the longest the club has had since the All-Star break.

“It's been tough,” said Cora. “And we’ve lost games in a lot of different ways. We've been talking about the offense lately, but I think they’ve done a good job bouncing back. At one point, it was the rotation. At another point, it was the bullpen. The other thing is the defense. We’ve been talking for three years about this. We have to take care of the baseball.”

Miscues again hurt Boston on Sunday. Jazz Chisholm Jr.’s line drive went off first baseman Connor Wong’s glove in the second inning, helping the Yankees score their first run of the game. With the Sox down by two in the seventh, Chisholm hit a tailor-made inning-ending double-play ball to Romy Gonzalez, who bobbled the ball as he was about to throw to second for the force. Boston got no outs on the play, and the Yankees added an insurance run later in the inning.

While the Red Sox had one of their best offensive games in weeks while knocking out Yankees ace Gerrit Cole in Saturday’s 7-1 victory, they went 0-for-9 with runners in scoring position while leaving eight on base against lefty starter Carlos Rodón and five relievers on Sunday.

“It wasn't like it was a bad series because we lost three out of four,” said Cora. “We were in every game. Every game was a close one, but that’s not enough in this league. You don’t get wins by playing tough games. You get W's when you win games. And we didn't do it.”

New York worked Kutter Crawford hard, as Boston’s righty starter threw 92 pitches (58 strikes) over 4 1/3 innings. The home run has been Crawford’s nemesis this season, and that was the case again in this one.

Gleyber Torres hit a Yankee Stadium special to right for a solo shot that made it 2-0 in the bottom of the third. The only other MLB ballpark it would have been a home run at, per Statcast? Houston’s Minute Maid Park.

Later in the frame, Aaron Judge mashed a majestic two-run homer to center that went a Statcast-projected 445 feet. Judge’s 53rd homer of the season gave his team a 4-0 edge.

“I just didn't make pitches when I needed to,” Crawford said. “Obviously, you can't throw Judge a 92 mph fastball right down the middle. I just didn't do my job today.”

Tyler O’Neill struck back for the Red Sox in the top of the fourth, belting a two-run homer to left-center against Rodón. Clutch hits wound up being elusive for the rest of the day.

It was O’Neill who hit the three-run walk-off homer against the Orioles in the 10th inning on Wednesday night, sending the Red Sox to the Bronx on a high note. But they lost the first two games in New York by a run, then battled back for a big win on Saturday only to go backward on getaway Sunday.

“Yeah, we're playing some good baseball, too,” said O’Neill. “Just things aren’t coming together right now, and obviously it's not a great time, so hopefully we'll clean things up quickly. Obviously, we want to make up ground as soon as possible. But, you know, there's still a chance for sure.”

Those chances, however, are dwindling.