Their offense silent -- as in no runs for 31 consecutive innings -- Victor Martinez hit a dramatic two-run homer off Yankees lefty Phil Coke with one out in the top of the eighth inning to give the Sox a 2-1 lead.
But the Yankees came back with two big back-to-back two-out blasts against Daniel Bard in the bottom of the eighth. Johnny Damon smacked the equalizer just over the wall in right-center. Up stepped Mark Teixeira, who hit a towering shot down the line in right that landed in the second deck.
"It was a quick change of emotions," said Red Sox manager Terry Francona. "We're not doing anything offensively and Alex [Rodriguez] hits the home run [to put them up 1-0]. It's a tough blow to take. Then we come back and Victor puts us ahead, and Bard comes in and, first two hitters in, really does what he's supposed to. Again, with not a lot of offense, we're feeling like, [we can] go ahead and win this game. It changed so fast. It was a big shift in emotions."
No matter what, it was the type of defeat that stings. But considering the circumstances of the past few days, this one was more painful.
The loss sent the reeling Sox 6 1/2 games behind the Yankees in the American League East. Boston is now tied with the Rangers for the lead in the Wild Card standings, and 1 1/2 games ahead of the Tampa Bay Rays.
"So we'll start over," said Red Sox second baseman Dustin Pedroia. "We've got a new season. [There are] 50-something games [left]. We're excited about it. It's a good opportunity."
Overall, the Red Sox have a season-high losing streak of six games. It was the first time Boston has been swept in a four-game series in the Bronx since 1985.
"We were winning the East, what, a week and a half ago? Anything can happen," said Pedroia. "We just need to find ways to win. It's been tough, obviously, the last six games, but we'll grind it out."
The AL East has already had wild swings in momentum this season, both in terms of head-to-head encounters and the race as a whole. The Red Sox led by five games on June 24. And they won their first eight games against the Yankees for the first time since 1912.
"It was so long ago when played them before," said Francona. "Regardless of whether we're beat up or we have changes in our roster, whoever we sent out there, they ended up beating us. That wasn't, certainly, our goal. We have to live with it and now move on."
Amid a brilliant pitchers' duel between Andy Pettitte and Jon Lester, Rodriguez had staked the Yankees to a 1-0 lead by roping a solo homer to center field to lead off the bottom of the seventh inning.
In a sense, it felt like a familiar nightmare when Rodriguez pummeled Lester's 94-mph fastball.
"I was trying to come in, and I left it out over the plate," said Lester. "You can't do that to a guy like that. He put a good swing on it. Would I take it back? No. It was the pitch I wanted to throw. I just didn't execute it."
In Friday night's 15-inning marathon, A-Rod was the one player who came up with a big hit on a night both offenses went nearly silent.
For a while, it looked like that might again be the case.
Pettitte had given the Yankees seven vintage innings, allowing five hits and no runs.
When the Yankees went to Coke, the Red Sox got some momentum. Dustin Pedroia smacked a one-out single and Martinez got hold of a 1-2 pitch and hammered it, setting off an eruption in the Boston dugout.
"Obviously, I was pretty happy about [the home run] putting my team on top and getting the lead," said Martinez. "But, unfortunately, we let Lester down. It was fun. It was a great feeling."
Upon Martinez's arrival back to the dugout, David Ortiz gave his new teammate a bear hug.
The Red Sox hoped it was just the jolt they needed to end the skid. It snapped the longest scoreless stretch by the Red Sox since the 1974 team went 34 innings without a run.
"We got the big hit there from Victor, we get up one run," said Pedroia. "We felt good about ourselves. It kind of happened really fast. We need breaks to win sometimes, and we didn't get any tonight and we haven't gotten any in a while, so we're excited to head back home and start fresh."
Bard just wanted to hand the ball to closer Jonathan Papelbon, but he couldn't execute to a couple of tough hitters.
"It's part of baseball," said Bard. "We're going to have ups and downs. I'm not perfect. I had a string of a lot of good innings in a row and I knew it was going to come to an end eventually. I'm not going to change everything, because they weren't terrible pitches. It's two really good hitters that sat on the right pitch at the right time."
Just like the Red Sox didn't think the Yankees were going anywhere even when they beat them eight times in a row, the same is true after this latest drastic change in momentum.
"That's a team that's been through a lot," said Yankees manager Joe Girardi. "There's a lot of players who have been down in [postseason] series and been able to come back. That's a club that I expect will bounce back and play very good ball. This division will go right down to the end."
"We do have a long part of our season left," said Red Sox catcher Jason Varitek. "This team, we have too many good characters on this team. This team won't quit."
Ortiz was asked if he had a message for Red Sox fans who might feel tempted to push the proverbial panic button.
"Stay positive," Ortiz said. "Things are gonna change. It can't get any worse, right? We're going to keep on fighting. There's nothing else you can do but play. We'll try to change things around. Everything's going really bad right now, but the next day, we'll come to the field and turn the page, come back and play."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.