HOUSTON — Manny Parra just can't seem to get past the middle innings.

The Milwaukee left-hander lasted four innings, giving up six runs, as the Brewers fell to the Houston Astros 6-2 Saturday night.

In six starts this season, Parra has never gone longer than 5 1⁄3 innings — he's done that twice — and left with four innings under his belt on three other occasions.

The 25-year-old Parra (1-2) allowed a career-high six runs and tied his career mark with nine hits allowed. He walked four and struck out three in four innings.

"He was consistently down with his other stuff, but for some reason, not his fastball," Brewers manager Ned Yost said. "That's the No. 1 prerequisite for a young pitcher: You've got to control your fastball. If you can't, you won't stay around very long."

Parra's real troubles Saturday began in the fifth inning when Houston pitcher Brandon Backe and Michael Bourn hit back-to-back home runs to spark a five-run outburst.

"The whole inning just started rolling," Parra said of the decisive fifth, when he allowed six hitters to reach safely before he was pulled. "I tried to slow it down. I wasn't able to do that."

It was the second night in a row the Astros have hit consecutive home runs, after they hit three straight in the series opener.

The score was tied at 1 before Backe hit the third home run of his career to the third row of the Crawford Boxes im left field. Bourn followed with a homer to right field that made it 3-1. Parra had only allowed one home run this season.

Backe and Bourne — exactly the Astros vaunted "Killer B's" of old — came in with five career home runs combined in 316 at-bats.

"It woke (our offense) up a little bit I guess," Backe said. "I think they were probably going to do it even if I didn't get that home run, but it helps out a little bit when your pitcher hits a home run."

Kaz Matsui followed the pair of homers with a single. He stole second base before scoring on a double by Miguel Tejada. Left fielder Ryan Braun dove to catch Tejada's fly ball, but it bounced off his glove and dribbled away.

Lance Berkman singled before Tejada scored on a wild pitch. Parra walked Carlos Lee before he was replaced by Dave Bush, who was brought up from Class AAA Nashville on Friday.

Hunter Pence's RBI single ended the scoring for the inning and Bush retired the next three batters to take it to the sixth.

Backe, who pitched 5 2⁄3 solid innings for his first win since April 12, allowed five hits and two runs with three strikeouts and five walks. His game got off to an inauspicious start when Rickie Weeks hit a leadoff homer. Mike Cameron then singled, but the Astros turned a double play before Prince Fielder grounded out to end the inning.

Backe pitched four straight scoreless innings before an RBI single by Corey Hart with one out in the sixth. Backe walked the first two batters in that inning to set up the score.

He was replaced by Oscar Villarreal with two outs after walking his third batter of the inning. Tony Gwynn grounded out to end that inning.

"I'm looking for those guys to be aggressive," Yost said. "(Villarreal) had come in and he's looking to get ahead. Tony is looking for him to throw a fastball, and he didn't."

Material from MLB.com was used in this report.