The Angels posted their seventh straight victory in an action-packed tilt that saw starter Jered Weaver last just 12 pitches before exiting with a back injury, while the Yankees' Phil Hughes was pounded for seven runs in an unsatisfying trip home.
Trumbo's walk-off blast was the first by an Angel against the Yankees since Tim Salmon hit one off Jim Abbott on April 28, 1993.
"I've faced Cory since 2005, so I have a pretty good idea of what he throws," Trumbo said. "He has really good stuff, too. I figured if I gave myself a couple swings, and as many chances as possible, it's the best way to go there."
Slumping catcher Russell Martin delivered a game-tying two-run double off Jason Isringhausen in the seventh inning, capping a frame in which the Yankees erased a three-run Angels advantage.
"It was a big at-bat to tie the game, but it doesn't really mean anything if you lose," Martin said.
Yankees relievers David Phelps and Boone Logan kept the game tied to the ninth, but New York couldn't capitalize on a bases-loaded chance facing Jordan Walden in their final opportunity.
Martin dribbled a grounder up the middle that shortstop Erick Aybar kept on the infield as Mark Teixeira had to hold at third base with the go-ahead run. Walden got Derek Jeter to ground into a fielder's choice for the third out.
"We had some chances," Yankees manager Joe Girardi said. "It's a game where we continued to fight back, and I liked our at-bats."
Hughes was taken off the hook for the decision after his ineffective outing, but it still marked an unhappy homecoming for the Tustin, Calif., product, as he was rocked for a career-high 11 hits.
"It was mainly the first inning, a lot of pitches were over the middle of the plate," Hughes said. "The offense did a great job today. They got some runs in the first and I gave them right back. That was tough."
Hughes didn't blame the long wait in the first inning, as Weaver exited for a date with an MRI tube and New York sent nine men to the plate in a three-run first inning after Bobby Cassevah was summoned from the bullpen.
"I was just trying to hit my spots and mix my pitches as best I could," Hughes said. "I tried to keep us in the game as best I could, and still giving up runs here, runs there."
The Angels' four-run first inning was highlighted by Howie Kendrick's go-ahead, two-run single. Kendrick added a third-inning sacrifice fly after a frightening collision between Nick Swisher and Curtis Granderson in right-center field.
"Both of us were reaching for the ball at the same time, and then just, kaboom," said Swisher, who was in pursuit of what would be a triple for Trumbo. "And next thing I know, I'm laying there on my back."
Both players stayed in the game. Mike Trout homered in the fourth, and an infield hit and sacrifice finished Hughes after 5 1/3 innings, in which most of the contact seemed to be consistently barreled up well by the Angels.
"He couldn't get his fastball to stay on the first-base side," Girardi said of Hughes. "If he would try to go away from righties, it would come back across. If he tried to go in to lefties, it would come back across. He really didn't have much command of it."
Cody Eppley and Phelps couldn't bail Hughes out from further damage, as Kendrys Morales jumped on Phelps' first-pitch breaking ball and laced a two-run double, giving the Halos an 8-5 lead.
Morales has struggled against left-handed pitching this year, but Girardi said he didn't want Clay Rapada in that spot and that it was not a spot to call on Logan, who was eventually used to retire Morales in the eighth inning.
"Boonie's one of the guys I use in the seventh and the eighth now, so I just felt it was too early," Girardi said.
Granderson blasted his team-leading 15th home run off Cassevah in the second inning and Teixeira delivered a towering solo shot, his fourth in four games and ninth overall, off Hisanori Takahashi in the fifth.
"You've got to go ahead and take advantage of situations early on in the game," Granderson said. "We weren't able to do that and they were able to stick around long enough. We had to fight back and sure enough, a great hitter coming up in the ninth inning was able to end it for them."