After Ryan Kalish led off the ninth with a single and Mike Aviles drew a walk, Nick Punto's job was to move the runners to second and third for the top of the order.
Instead, Punto popped up the bunt, and first baseman Chris Carter caught it with a nice diving stop and fired to first, where Aviles was doubled off.
"You can't bunt into the double play there," said manager Bobby Valentine. "That simple. We had our best bunter on the team up. He's got to be able to bunt the ball and get the guys over."
Nobody felt worse about it than Punto, who prides himself on being able to do the little things.
"Simple execution play that I didn't get down," said Punto. "That's what I do. That's a simple fundamental. You can't make those mistakes."
He wasn't alone. After that ill-timed double play, Kalish, who wasn't being held at second, tried to steal third.
Though replays indicated he might have been safe, Kalish was ruled out, and the inning was over.
"Aggressive play," said Valentine. "They blocked the base on him. He had it stolen easily. When the base was blocked, he couldn't get in there. Good play on their part. Bad play on ours."
The play was Kalish's idea -- not Valentine's.
"Well, I didn't hold him. I wasn't expecting a steal, but if I don't want him to go, I better hold him," Valentine said. "It was an easy steal. Big leg kick, knew he could make it. He just couldn't get by the guy's leg."
Kalish's misfortune wasn't over yet.
Then came the bottom of the ninth, which closer Alfredo Aceves opened by giving up a single to left by Carter. With one out, Cliff Pennington lofted a single into left-center, and the A's had first and second with one out.
Up stepped pinch-hitter Brandon Moss, and he ripped a single up the middle on an 0-2 pitch from Aceves. Kalish, in his haste to try to cut down the tying run at the plate, bobbled the ball. The error allowed Pennington to move to third, putting him in position to score the walk-off run.
Crisp's fly ball to right-center was easily deep enough to end the game. Kalish caught the ball on the fly, but he had no chance. After a fruitless throw home, he walked off the field in frustration with his teammates.
"I've got to play better defense. That's the bottom line. I didn't get called up [to do that]," Kalish said. "That's what I need to do the best of, and right now I'm just not doing it."
Kalish admitted he might have taken his eye off the hit by Moss just for a second so he could size up the baserunners.
"For sure, between that and the ball out there kind of snakes a little bit. That was something in the last two days with BP, taking ground balls, you see. Like I said, I've got to play better D," Kalish said.
Once the game was over, the top of the ninth only stung more.
"Oh, we had first and second, no outs, top of the ninth. That's where the game was lost," Valentine said.
The game was lost because the Red Sox again didn't hit. Entering Wednesday's finale of this road trip, Boston is 2-4 against two teams below .500. The club's bats have scored 12 runs over the six games.
"Just sputtering a bit, yeah," Valentine said. "You know, not stringing the hits together. We will tomorrow."
The Red Sox got a terrific performance from Jon Lester in this one. Lester gave up just one run for the first time since May 19. He equaled a season high with nine strikeouts, giving up four hits.
If the 6 2/3 frames made the performance seem like less than vintage Lester, consider he lasted that long after laboring through a 31-pitch first inning.
Just three pitches into his start, Lester surrendered a leadoff homer to former teammate Crisp. In fact, Crisp became the third ex-Boston outfielder to homer in the series, joining Josh Reddick and Moss.
But Lester mowed through Oakland's offense the rest of the way, finishing with 107 pitches.
"I feel good," said Lester. "I didn't feel like I threw the ball any different from the last couple starts. When I needed to make pitches, I did. I fell behind Coco in the first, [and] he put a good swing on a ball that was middle in. That was the only damage. I just was able to execute pitches. That's what it always ends up coming down to in the end."
Vicente Padilla walked a tightrope in the eighth inning. Aviles misplayed Kurt Suzuki's line drive for an error and Crisp battled back from an 0-2 hole with a single. Weeks sacrificed the duo into scoring position, bringing up the dangerous Reddick, who has 19 homers.
Valentine elected to load the bases and intentionally walked the former Boston outfielder. Padilla reared back and struck out Yoenis Cespedes and Jonny Gomes to escape the bases-loaded jam.
"Padilla was great. Jonny Lester was really good," Valentine said. "That's about all we've got to say. Those are the good things. I like the good things."
However, Valentine seemed more agitated by this loss than most, slamming a bottle cap up and down on his desk repeatedly.
"I don't like to lose," Valentine said. "That's what bothers me the most."