Jarrod Parker's best start in more than two weeks couldn't prevent the suddenly punchless Athletics from dropping their second straight game.
Now Oakland's slim lead in the wild-card race is gone and manager Bob Melvin's team is on the verge of being swept at home for the first time since late May.
Brandon Moss homered but the A's couldn't manage anything else against Los Angeles pitcher Zack Greinke in a 6-1 loss to the Angels on Tuesday night.
"Every game is big right now," said Parker, who took the loss despite pitching seven strong innings. "We don't want to be on the losing end of anything. I think when we set back up tomorrow we have a pretty good chance of taking a game (but) every game is important at this point."
The A's have dropped two straight to the Angels following a nine-game winning streak. That dropped Oakland into a tie for the wild-card lead, four games behind first-place Texas in the AL West and 3½ ahead of the third-place Angels.
Since scoring 57 runs in seven games while sweeping Cleveland and Boston, the A's have been outscored 14-4 by Los Angeles.
Oakland needs to win in Wednesday's series finale to avoid being swept at home since dropping three straight to the Yankees from May 25-27
"Each and every game is important here in September, but they come in and take the first two games from us I think it's just as important to win the game tomorrow," Melvin said.
Greinke pitched seven sharp innings to win his third consecutive start and Kendrys Morales had three hits and an RBI for the Angels, who remained 3½ games out of a wild-card spot in the American League. Los Angeles has won four of five on its six-game road trip and 11 of 14 overall.
Greinke (4-2) scattered four hits, struck out four and walked two. He also got some help from the Angels' defense when Mike Trout ran down Josh Reddick's deep fly to center in the sixth.
Since beginning his Los Angeles career with two losses in five starts following a July 27 trade from Milwaukee, Greinke has settled into a groove. He's yielded four runs over his last 21 2-3 innings and has gone at least seven innings in each of his last three starts.
Parker, who also lost to the Angels in his previous start at the Oakland Coliseum on Aug. 6, didn't pitch poorly but had nothing to show for it after going seven innings. He struck out Torii Hunter three times, had five strikeouts overall and didn't walk a batter for the second time this season.
"I pitched myself out of a couple jams and had pretty good stuff tonight, but all in all we lost," Parker said. "(Greinke's) got great stuff and you know that when any of those guys over out there go out to the mound you got to be on your game and basically go blow-for-blow and we tried to do that."
The Angels put runners on base early against Parker (9-8) but didn't break through until the fifth.
Alberto Callaspo and Chris Iannetta singled to put runners on the corners with one out before Trout hit a first-pitch RBI single up the middle. That gave Trout, a leading contender for AL MVP and Rookie of the Year, 75 RBIs.
Los Angeles opened the sixth with consecutive singles by Morales and Howie Kendrick. Both runners moved up on a sacrifice, and Morales scored on Callaspo's sacrifice fly to make it 2-0.
Greinke didn't need much else.
He worked out of a two-on, two-out jam in the first, stranded a runner at second in the third and retired 16 of 18 until Moss homered leading off the seventh. It was Moss' 16th home run this season and fourth in the last eight games.
Scott Downs pitched the eighth and Jason Isringhausen worked the ninth to complete the four-hitter for the Angels.
The Angels added a pair of insurance runs in the eighth off reliever Sean Doolittle, then scored two more in the ninth — one on a double by Morales.
NOTES: Albert Pujols doubled in the first to extend his hitting streak to 13 games. The Angels' slugger needs six doubles to reach 500. ... The A's recalled RHP Jim Miller from Class-A Stockton before the game. It is Miller's fifth stint with the big league club this year. ... Angels RHP Dan Haren (9-10) tries to snap a three-game losing streak to his former club when he pitches in the series finale Wednesday. RHP Brandon McCarthy (8-5) goes for the A's. ... Reddick was selected American League player of the week after going 12 for 31 with three home runs and 10 RBIs.