When Trout stepped to the plate, the Angels had runners at first and second with one out.
Alfredo Aceves, back on the mound after a three-game suspension, worked the count to 0-2. He then came up and in with a fastball, but Trout got just enough of it to get it by the dive of second baseman Dustin Pedroia and into center for the game-tying hit.
"He's a great player," said manager Bobby Valentine. "One of the best players I've seen in a long time. I thought we had him there in the last [inning]. Two fastballs by him in, and broke his bat on the third one. But good hitters get hits on broken bats."
Torii Hunter is also a good hitter, and he ended the game, lofting a sacrifice fly to deep center that Jacoby Ellsbury had no chance to make a play on.
"I just told myself, 'Just try to get a pitch up.' Unfortunately the first pitch was down, and I swung at it and he threw me a nice little cutter," said Hunter. "I just told myself, 'Just get something up and don't do too much, don't swing too hard. Just poke it in the outfield and we'll win this game.' So I just, 'Kept it simple, stupid,' and it worked."
Aceves had been suspended by the Red Sox for disciplinary reasons, stemming from his decision to storm into Valentine's office after not being used in a save situation on Aug. 24.
In this one, with Valentine's bullpen spent, he had little choice but to use Aceves for the eighth and ninth. After Aceves breezed through the eighth, the Angels got some life with one out in the ninth when Erick Aybar had a pitch glance off his foot.
"I'm not 100 percent sure it got the guy, but you can't go back and change it now," said catcher Ryan Lavarnway. "That kind of started a little bit of momentum that we didn't want to happen, and unfortunately we're talking about a loss instead of a win."
Aceves has struggled mightily of late, as this was his fourth blown save in his last seven opportunities.
"I'm not saying that was his role tonight for a save," Valentine said. "He was the only guy available to pitch."
The loss dropped the Red Sox 10 games back in the American League Wild Card standings.
Clay Buchholz was in position to get the win, leaving with a 5-4 lead.
The righty scattered six hits and four runs over seven innings, walking three and striking out five.
In the seventh, Buchholz had to stare down Albert Pujols with the tying run at second and two outs. Buchholz got the job done, inducing Pujols with a flyout to right.
"He really settled down," said Lavarnway. "He had four pitches working today, and in the first inning, maybe two bad pitches that got hit hard. After that, he really settled in and gave us a real good chance to win today."
The Angels jumped out quickly as Trout belted Buchholz's second pitch of the game over the wall in left-center for a leadoff homer.
"They call him 'The Natural' on TV. That's the closest thing I can say," said Buchholz. "He can run and throw and hit and hit for power, hit for average. It's fun to watch him play, just not when you're pitching to him."
Mark Trumbo added a sacrifice fly later in the inning, giving his team a 2-0 lead.
The Red Sox got a run back with one swing in the second, as Jarrod Saltalamacchia smoked a solo shot over the wall in right, his 22nd of the season.
"I feel good at the plate," said Saltalamacchia. "I've been feeling good. Just trying to put a few hits together. We're at that point where we're just grinding through, having to have good at-bats, trying to help the team in any way."
In the fourth, Boston put together a sustained rally against Angels ace Jered Weaver. Pedroia and Ellsbury started it with singles and Lavarnway worked a walk to load the bases. James Loney tied it with an RBI single and Saltalamacchia gave the Red Sox a 3-2 lead with an RBI single. Ryan Kalish hit into a double play, and another run scored.
Lavarnway gave Buchholz an insurance run in the sixth with a sacrifice fly.
But the Angels came storming back in the bottom of the sixth. Albert Pujols hammered a solo homer to center with one out to make it a 5-3 game. With two outs, Buchholz walked Trumbo. Up next was Howard Kendrick, and he rifled an RBI double that slimmed Boston's lead to a run.