Lackey (11-2) gave up seven hits and struck out five without a walk, allowing one runner as far as second base while lowering his ERA from 3.09 to 2.95. He lost the shutout bid when Jack Cust drove the right-hander's 91st pitch of the game to center field for his 23rd home run.
Lackey, who led the AL with a 3.01 ERA last year before strained triceps sidelined him for the first 41 games this season, improved his career record against Oakland to 14-3 and won his 10th straight decision against AL West teams. The complete game was his third this season.
Greg Smith (6-13) gave up five runs and a career-worst 10 hits over six innings, slipping to 1-3 against the division-leading Angels this season.
The rookie left-hander, who beat the Angels 6-1 on June 30 at Anaheim with a four-hitter for his first complete game victory in the majors, is 1-7 with a 4.72 ERA in his 10 starts since. Smith's loss total is the third-highest by an Oakland rookie behind Rick Langford's 19 in 1977 and Matt Keough's 15 in 1978.
Hunter, who came in 0-for-9 against Smith, had a hit in each of his first three plate appearances. He had an RBI double during a four-run third that enabled the Angels to grab a 4-0 lead. The Angels survived a scare during the rally when Hunter was struck in the head by a thrown ball while running the bases.
Mark Teixeira drove in the first run with a single, was held at third on Hunter's double and scored on Juan Rivera's sacrifice fly. Right fielder Carlos Gonzalez's throw toward the plate was cut off by first baseman Daric Barton, whose throw to third ricocheted off the left side of Hunter's helmet as he slid into the bag.
Manager Mike Scioscia and trainer Ned Bergert came out to check on the Gold Glove center fielder, who appeared to be too woozy to continue. But Bergert allowed Hunter to stay in the game after helping him to his feet and moving his index finger in front of Hunter's face.
The Angels were already short two outfielders, with Vladimir Guerrero getting his second straight day off under Scioscia's insistence, and Garret Anderson resting his sore left knee. Hunter scored on a single by Gary Matthews Jr. that capped the rally, and Howie Kendrick made it 5-0 in the fourth with an RBI single after a leadoff double by Mike Napoli.
The Athletics trailed the Angels by just four games after beating them on July 11 in Oakland, but since then have gone 9-30 to fall 20 1/2 games off the pace.
Notes:@ Tuesday's announcement that video replay will begin on Thursday received a mixed response from the Angels and Athletics -- two of the three teams that will be playing at home that night. "I think it's great for the game," Oakland DH Frank Thomas said. "It's used in other sports, so I don't know why baseball was opposed to it. Yes, we've dealt with the human element for a long time in baseball, but there have been a lot of bad calls over the years that, I'm sure the umpires didn't go home and sleep well after seeing it on replay. I've lost a couple of home runs over the years that were called foul. But I just think it's always right to make the right call, for all parties." ... Hunter took the other side of the issue: "I'm an old-school guy, and I still feel that it's the umpires' call to make -- whether it's the right one or the wrong one. The human element is what makes baseball so great and so much fun, because with the naked eye, you can either make it right or make it wrong."