In the 10th, the A’s slipped another game behind the Angels in the exciting AL West race.

Howie Kendrick drove in Albert Pujols with a sacrifice fly in the 10th, and Los Angeles opened a two-game lead atop the major league standings with a 4-3 victory Thursday night.

Josh Hamilton had a 10th-inning single as the Angels (80-53) edged Oakland (78-55) to begin a four-game series between the California clubs with the majors’ two best records.

They’ve already got a rivalry, and the postseason stakes — along with a crazy play at first base — make it even more exciting.

“I think that’s our fourth extra-inning game here,” reliever Dan Otero said. “They’re a great ballclub, and we know we are, too, so it’s a battle every time out. They’re going to battle us to the end, and we know we’re going to give it all we’ve got.”

Oakland protested the game after Erick Aybar hit a short chopper up the first-base line to open the ninth. He ran into Otero as the pitcher fielded it and bumped into first baseman Brandon Moss.

Home plate umpire Greg Gibson immediately awarded first base to Aybar, prompting a lengthy argument from A’s manager Bob Melvin. The Angels then loaded the bases with one out, but Kole Calhoun popped up and Mike Trout grounded to third against Cook.

Melvin thinks Aybar went out of the baseline and tried to hit the fielder.

“I thought they would overturn it, based on what we were seeing,” Melvin said. “It was pretty evident.”

Angels manager Mike Scioscia disagreed, saying Aybar “had nowhere to go.”

Crew chief Gerry Davis said the obstruction ruling was a judgment call by Gibson. Judgment calls can’t be protested, according to Rule 4.19.

Pujols drew a leadoff walk from Ryan Cook (1-2) in the 10th, and Hamilton moved him to third with a bouncing hit up the middle.

Kendrick’s long fly to right easily drove in the slow-footed Pujols, setting off a playoff-worthy celebration by the Angels, who have won 12 of 16.

“Every time we play these guys, it’s a great game,” said Kendrick, who also had two hits. “We’ve already had a few walk-offs against these guys. We know we’ve got to play them … down the stretch.”

The A’s took two of three from the Angels at the Coliseum last week. The clubs also begin the final week of the regular season with a three-game series in Oakland.