Anderson was solid early, allowing just two hits through the first four innings, before running into some trouble in the fifth.
He allowed singles to Howard Kendrick and Jeff Mathis before Chone Figgins hit an RBI double that left runners on second and third. The A's got a break when Mathis was thrown out at home on a hard grounder to first baseman Daric Barton, but Hunter came to the plate with runners at first and third.
Hunter didn't waste any time, hitting the first pitch over the left-field fence to give the Angels a 4-1 lead that they would only build on later in the game, including a five-run eighth inning.
"The pitch was supposed to be inside, running in on him, but he left it up and over the plate," Oakland manager Bob Geren said. "It might've even been a ball, but he got on top of it. Torii Hunter is a good player, and that's his strength right there."
The homer came on a high fastball, which was the same pitch Anderson struck Hunter out on in the first inning.
"That was the pitch of the game. [It was] the game-changer right there, not executing that pitch," Anderson said of the homer. "In the at-bat before that, I struck him out on a pitch higher than that."
The long ball gave the Angels all the offense they needed behind right-hander John Lackey, who won his 100th game and continued his dominance of the A's in his career.
Lackey allowed just one unearned run on five hits over eight innings to improve to 16-4 lifetime against Oakland.
"He pitched a good game," Barton said. "He battled and threw his offspeed stuff for strikes, too. So if you're looking for a certain thing, he mixes it up real well."
Lackey, who also pitched when Anderson nearly had his no-hitter against the Angels, again was impressed by the 21-year-old lefty's stuff.
"His stuff jumps out at you," Lackey said. "He's over 95 [mph] with a hammer. He's gonna be a good one, no doubt about it. Last time we faced him, in Oakland, he was tough. Kid's got good stuff."
The A's got on the board first, plating a run against Lackey in the third inning. Barton singled and Eric Patterson doubled, putting runners at second and third. Lackey then threw to shortstop Erick Aybar in an attempt to pick off Patterson, but the throw was bobbled, allowing Barton to score.
That was the only run of the game for the A's, who went 0-for-4 with runners in scoring position.
"We didn't get a whole lot off him," Geren said of Lackey. "We had a couple hits, but even when we scored, it was on an error. He threw the ball well."
The Angels later blew the game open with a five-run eighth inning powered by a three-run homer by Kendry Morales off reliever Jay Marshall. It was Morales' 30th homer of the season and his third in the series.
"He had a very good series," Geren said. "We'll have to reevaluate him and how we're pitching him to see if it's the pitches he's seeing or if they're mistakes."
Marshall was hit hard in the eighth, allowing five straight hits with two outs before being relieved by Santiago Casilla. Casilla then hit Jeff Mathis with a pitch before allowing an RBI single to Figgins to make it seven straight Angels reaching base in the inning with two outs. Casilla got Aybar to ground out to end the inning, but the damage was done.
Despite the loss, the A's could take some solace in earning a split against the first-place Angels in a four-game series at Angel Stadium.
"We battled pretty good, so we can take that to the end of the season and progress with that," Anderson said. "Any time you play a team of that caliber and you split with them, it's going to be a good series."