Lester had been belted around by the Yankees throughout his 2 1/3-inning stint, which ended with one last indignity, a line drive off Melky Cabrera's bat that scorched off the left-hander's right leg, perhaps just inches from a direct hit of his knee cap.
The one positive development the Red Sox could take from the night? X-rays taken on Lester proved to be negative. Boston's star southpaw was diagnosed with a contusion of his right quad and is day-to-day. Lester threw 78 pitches, allowing eight hits and five runs while pitching fewer than six innings for the first time since July 30.
"Any time they hit a ball off any part of your body, you're worried. But everything came back fine. We'll treat it and go from there," said Lester, who said he intends to make his next start on Thursday at Fenway Park against the Indians.
Despite the loss, the Red Sox are still in strong position to clinch their sixth postseason berth in the past seven years. With nine games left, Boston has a magic number of three to eliminate the Rangers in the American League Wild Card standings. Meanwhile, the Yankees have a magic number of three to clinch the AL East.
Boston won the first eight games of its season series against New York, but the Yankees have won seven of the past eight.
Joba Chamberlain earned the win for the Yankees, allowing five hits and three runs over six innings and striking out five. But he had pretty much mastered the Boston bats until the top of the sixth, when a two-run homer to left by the red-hot David Ortiz cut New York's lead to 6-3. It was Ortiz's third long ball in the past three games, and he has 27 homers and 94 RBIs on the season.
But the Red Sox couldn't get any other legitimate damage against Chamberlain.
"He did a good job of keeping his breaking ball over for strikes early on," said Red Sox left fielder Jason Bay. "He did a good job of mixing things up. In the past starts, he's had some trouble getting going in the first inning or two. Tonight, he was good right from the get-go."
The Red Sox had other problems as well. The Yankees ran roughshod around the bases, stealing seven bases. Red Sox manager Terry Francona didn't think catcher Jason Varitek deserved the blame for New York's successful running attack.
"Well, with [the] left-hander, they go first move," Francona said. "There's not a lot the catcher can do there."
But the Yankees opened it back up with two insurance runs against Michael Bowden in the bottom of the sixth.
While Chamberlain came out blazing, it was clear immediately that Lester didn't have his best stuff. Derek Jeter led off the first with a single up the middle and stole second. Alex Rodriguez drove in Jeter with an RBI single to left-center, making it 1-0.
Lester navigated out of traffic in the second, but he was not so fortunate in the third. After a leadoff single by Mark Teixeira, A-Rod unloaded for a two-out homer. The hits kept coming from there. Hideki Matsui singled, and Robinson Cano rifled a double to right one batter later. Nick Swisher walked to load the bases, setting up Cabrera, who ended Lester's night with the line drive off his right leg for an RBI single.
"I knew he was in pain," said Ortiz. "Melky put a good swing on the pitch. Not too much you can say. But he's fine."
As for the way Lester pitched?
"I felt like my stuff was good," Lester said. "It was one of those nights where they made it seem like I didn't. I thought I had a good curveball. I don't know if I was just trying to do too much with the stuff that I thought I had. They just turned it around and got some runs."
The Yankees pretty much agreed with Lester's assessment.
"We hit a couple good pitches and put the ball in play," said Rodriguez. "I think any great pitcher, you want to get him the first two or three innings. We did that tonight."
Fortunately for the Red Sox, Lester was down, but hardly out.
"You know what, he's going to be OK," Francona said. "When it first happened, I think it looked terrible. It sounded terrible. He was in a lot of pain. I think it caught enough meat and muscle where it wasn't just a direct blow on that bone."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.