BOSTON -- Garrett Richards said it was no big deal pitching at Fenway Park for the first time since suffering a devastating knee injury there last August.

Instead, the Los Angeles Angels ace was thinking more about the runs he gave up after his team scored nine in the fifth inning en route to a 12-5 win over the struggling Boston Red Sox.

"I gotta be better than that," the right-hander said after having to leave with the bases loaded, nobody out and two runs home in the seventh inning. "Having a lead like that, you don't want to get caught just pitching to contact and stay competitive ... tonight was one of those nights."

The Angels, who have been struggling offensively all season, broke through with a 39-minute fifth that saw catcher Chris Iannetta hit a three-run homer and shortstop Erick Aybar add a two-run shot to build an 11-3 lead.

It was last Aug. 20 that Richards, on his way to Cy Young Award consideration, suffered a ruptured left patellar tendon covering first base against the Red Sox. He missed the rest of the season and was still out for the first 15 games of 2015. But he's back and he's already run up a 4-2 record.

He had a streak of five straight quality starts snapped Friday but got another win, with left-handed reliever Jose Alvarez keeping more runs from scoring with a strikeout and a double play.

And yes, Richards even covered first on a groundout that ended the fifth. Pitching back at Fenway seemed like the furthest thing from his mind and he was happy with the win.

"I think Garrett threw the ball maybe a little better than his line showed," said manager Mike Scioscia, who cited the wait during long innings as a hazard for his pitcher.

It was the first time the Angels, who came in next to last in the American League in hitting, scored nine runs in an inning since April 20, 2013 against Detroit -- and Porcello.

Center fielder Mike Trout, who had two hits and an incredible steal of third in the inning, finished with three singles and also threw Boston first baseman Mike Napoli out at the plate with a one-bounce throw from the warning track in left-center. The swipe of third featured Trout avoiding the tag, something Scioscia said was right out of "The Matrix." Trout was called out but it was overturned.

First baseman Albert Pujols hit a solo homer and a pop fly double as the Angels, who won all four games at Fenway last season, improved to 22-20.

Napoli hit a solo homer for the Red Sox, who dropped their third straight and fell to 19-22. They have made five errors and had three baserunning blunders in the past two games.

"We're not playing very good. I wish I had a magic word," said second baseman Dustin Pedroia, who had three singles and an RBI. "It's baseball -- you can't flip a switch. You gotta put the work in and then play better."

Porcello had been pitching well and shut the Angels out through three. But after Pujols keyed a two-run fourth, the right-hander walked the first two in the fifth to start the carousel.

"Fifth inning I hit a wall, walked the first two guys and couldn't recover from it," he said. "I take full responsibility for the loss today. That was completely on me. I gotta be better."

Both Porcello and reliever Matt Barnes were knocked out for the game in the big fifth.

Third baseman Brock Holt had a two-run double for Boston.

NOTES: OF Rusney Castillo, recalled from Triple-A by Boston earlier in the day, was 1-for-4 and dropped a fly ball. ... The home fans, who cheered wildly when Castillo caught a fly ball hit by the next hitter, became so bored they started a "Free Tom Brady" chant, honoring the embattled quarterback. ... Boston LF Hanley Ramirez left the game in the sixth inning with left hand soreness from getting hit by a pitch in the fourth. He will be checked Saturday. ... OF Jackie Bradley Jr. was returned to Triple-A Pawtucket to make room for Castillo. ... Talking Thursday about his left knee injury suffered at Fenway, Richards said, "It sounded like a Pillsbury biscuits tube, you know, when you open it and it explodes? … It was gross." ... 3B Pablo Sandoval (knee bruise) and RF Shane Victorino (calf) remained out of the Boston lineup in day-to-day situations. ... Angels LHP C.J. Wilson pitches in the second game of the series Saturday night against Red Sox RHP Steven Wright, the second knuckleballer the Angels face in three days after R.A. Dickey on Thursday.