OAKLAND -- The Angels' first grand slam of the season came from an unlikely source.
Kaleb Cowart, who entered Tuesday batting .123 in 73 at-bats this year, crushed his first career grand slam off Lou Trivino to cap a six-run sixth inning that helped propel the Angels to a 9-7 series-opening win over the A's at the Coliseum.
"It was good to have a good night like this, for sure," Cowart said.
The A's, whose magic number remained at seven, took a 4-1 lead into the sixth. But the Angels came back to load the bases with one out after Jose Fernandez walked and Justin Upton and Shohei Ohtani singled. Oakland manager Bob Melvin brought in Trivino to face Andrelton Simmons, who lifted a first-pitch fastball out toward right field that sliced into foul territory.
The A's challenged the call after a spectator reached for the ball from the stands, potentially obstructing right fielder Stephen Piscotty from making the catch, but a replay review determined that no fan interference had occurred. Three pitches later, Simmons lined a two-run single to center field to cut the deficit to one run.
Piscotty said that he felt he could have made the catch, had the fan not disrupted his route to the ball.
"It's a tough play going into the wall, but I felt like I was there with enough time," Piscotty said. "It definitely changes how that inning goes, but nothing you can do about it now."
Trivino hit Taylor Ward with a pitch to load the bases for Cowart, who launched a 1-0 fastball to right field for his first home run of the season, giving the Angels a 7-4 lead. Cowart drove in another run with an eighth-inning triple to finish 2-for-4 with five RBIs.
"This guy works as hard as anybody in this game," Angels manager Mike Scioscia said. "It's good to see him get rewarded tonight with two huge hits for us."
With David Fletcher sidelined by a left hamstring strain, Cowart will likely get the majority of starts at second base over the final two weeks of the season, giving him more opportunities to finish a frustrating year on a high note.
"It's unfortunate what happened to Fletcher, but I'm going to embrace the opportunity that's in front of me and just go from there," Cowart said.
Michael Trout also homered for the Angels, while Simmons went 3-for-4 with two RBIs and two runs scored.
Left-hander Tyler Skaggs pitched three hitless innings in his first start for the Angels since Aug. 11. Skaggs, who missed 32 games with a left adductor strain, issued only a pair of walks and struck out three before departing after throwing 51 pitches.
"I felt pretty strong today," said Skaggs, who lowered his ERA to 3.69. "My mechanics felt great. Fastball command was really good. Changeup, not so much. But I felt pretty strong out there."
MOMENT THAT MATTERED
Buttrey halts A's rally: The Angels padded their lead by scoring a pair of runs in the eighth on a throwing error by Oakland third baseman Matt Chapman and Cowart's RBI triple, and those insurance runs proved key after the A's scored three runs to cut their deficit to 9-7 in the bottom of the inning.
Lowrie ignited the rally by drawing his third walk of the night, and Piscotty and Matt Olson followed with consecutive singles off Justin Anderson to make it 9-5. After walking Marcus Semien to load the bases, Anderson was replaced by Ty Buttrey, who yielded a two-out, two-run single to pinch-hitter Dustin Fowler before coaxing a groundout from Ramon Laureano to end the threat.
Buttrey returned to the mound in the ninth and pitched a perfect inning to convert a five-out save. The 25-year-old rookie has a 0.59 ERA over 15 1/3 innings this season.
"Every time Ty is challenged, he responds very well," Scioscia said. "He came in there, bases loaded, and kept the lead for us, which was big. And then finished off the ninth. He's starting to get comfortable and, obviously, we're taking notice of him. It's another great outing for him."
After Cowart's blast, the Giants are the only team in the Majors without a grand slam this season.
Angels right-hander Felix Pena (3-4, 3.75 ERA) will oppose A's left-hander Brett Anderson (3-5, 4.35) on Wednesday as the three-game series continues at 7:05 p.m. PT at the Coliseum. Pena has a 2.76 ERA over his last eight outings. He gave up three runs over 5 2/3 innings in his last start against the A's on Aug. 10.