"We had a good game today," said Aceves. "Unfortunately, we didn't get the win. That's all I can say."
When the Tigers started their winning rally, Mark Melancon was on the mound for the Sox.
Jhonny Peralta got things going by looping a one-out single in front of right fielder Ryan Sweeney. Alex Avila stepped up next and dropped one in front of left fielder Cody Ross.
Out came Valentine, and in came Aceves.
With Andrew Bailey out for several months following right thumb surgery, Aceves was installed as Boston's closer on Wednesday.
The righty's tenure as closer opened with bad luck, as he hit Ramon Santiago on the back leg with a 1-1 curveball.
"A breaking pitch. First cutter, then I go up with fastball, then I say it's a good situation to throw a curveball," Aceves said. "I throw a curveball, I miss my spot and I hit him."
Up stepped Jackson, and he stung it down the line in left, out of the reach of diving third baseman Nick Punto to end it.
"Well, it's a tie game on the road, so Melancon's going to try to get us [through the] inning," said Valentine. "As soon as it got to be a jeopardy situation, I just wanted to close the door with the last guy who's going to really be the closer. I thought he had the stuff to get a ground ball. He got a ground ball."
It seemed unlikely the Red Sox would even get to the bottom of the ninth after being overpowered for eight innings by Tigers ace Justin Verlander.
But Boston dug itself out of a 2-0 hole with a stirring ninth-inning rally against Detroit closer Jose Valverde, who was a perfect 49-for-49 in saves last year.
"The only thing that matters right now is winning," said Valverde. "That's it. Nothing you can do. It would happen one day, you know what I mean?"
Dustin Pedroia started it with a double to right-center. Adrian Gonzalez lined an opposite-field single to left to put runners at the corners with nobody out. David Ortiz got his team within one on a sacrifice fly to center. Darnell McDonald, on as a pinch-runner for Gonzalez, stole second.
That gave Sweeney the chance to be a hero in his Red Sox debut, and he pummeled a 2-1 pitch off the wall in right for the game-tying triple.
"He fell behind 2-0 and threw me an elevated fastball and threw me a split-finger down and in, and I put a good swing on it," Sweeney said. "I thought I got it at first when I hit it, but it just hit off the wall and it got away from him and I made it to third."
Jon Lester gave the Red Sox everything they hoped. The lefty went seven strong innings, scattering six hits and just one run. He walked three and struck out four, throwing 107 pitches.
"Lester was terrific," Valentine said. "Jonny did just what he needed to do. He went out there and put up innings and he did a great job."
Lester just had the misfortune of going against Verlander, which is why he left in a 1-0 hole and wound up with a no-decision.
Speaking of Verlander, he was downright filthy. The righty yielded just two hits over his eight innings, walking one and striking out seven.
"Every pitch he throws could be the best pitch in baseball," Pedroia said. "He's got great stuff and keeps the ball out of the middle of the zone, too."
The string of zeroes between the two star pitchers finally ended in the bottom of the seventh, when the Tigers rallied with two outs and nobody on.
Peralta lined a double to left and Avila followed by belting a 3-2 fastball into the left-field corner and over the head of Ross for an RBI double. Lester appeared to think he struck Avila out on a 2-2, 93-mph fastball, but home-plate umpire Dale Scott thought otherwise, leading to the full count.
"I made one mistake," Lester said. "Against a guy like that, that's what beats you."
In this one, however, the Red Sox were ultimately beaten in the back end of the bullpen.
"Like I said, it's just frustrating, especially after we come back," Melancon said. "Pedey gets on with that double. The offense has just been grinding through it the whole game and they come through and do their job in a clutch situation. It was great and fun to watch and exciting out there. To end up losing is tough."