The loss halted the Astros' season-best winning streak at three games.
"Any time you give up seven runs in three innings, it's just a bad start," Fiers said. "I didn't give our team a chance to do anything, really."
Fiers' ERA ballooned to 5.20, and the veteran right-hander missed tying his career-worst outing by one run. He gave up eight runs to the Rockies in Colorado on Aug. 31, 2012.
"First two innings he was pretty sharp, 20 pitches. In the third, he had a hard time going down and away," manager A.J. Hinch said. "It just looked like things unraveled."
Fiers' strength this season has been his control. In retiring the first six Angels though two innings, he got ahead in the count against the first five, and Johnny Giavotella popped out on the first pitch.
Rookie Rafael Ortega opened the bottom of the third with a double, and Carlos Perez singled him to third. Then Fiers, who rarely walks anyone, passed No. 9 Gregorio Petit to load the bases, setting the table for the dangerous top of the Angels batting order.
"Walking Petit enabled them to turn their lineup over," said Hinch, who, in his pregame media session, had pointed out the strength of the top and middle of the Angels lineup.
Fiers retired leadoff man Yunel Escobar on a foul fly, then fell behind Kole Calhoun, 2-0. That brought pitching coach Brent Strom to the mound for a consultation, but Calhoun lined the next pitch for an opposite-field RBI single, keeping the bases loaded. Mike Trout was hunting on the first pitch to him, and lined a bases-clearing double to left-center. Albert Pujols followed with career home run No. 570.
"I just gave up a couple of bloop hits to the bottom of the order," Fiers said, "then a couple of big hits to Trout and Pujols to open it up.
"They came out swinging from the start. I've just got to make better pitches. I didn't show them any curveballs at all, and I think they really capitalized."
Fiers walked just two in the abbreviated outing, extending his streak to all nine starts this season with two or fewer bases on balls. But the curveball never materializing, and his inability to get ahead after the second inning, proved to be his undoing.