HOUSTON (AP) - The Houston Astros began the second half of the season the same way they did the first.

With a loss.

The Astros lost 4-0 to the Pittsburgh Pirates on Friday night to begin a six-game homestand, casualties of a masterful performance by Jeff Karstens, who pitched a five-hitter for his second career shutout and first since 2008.

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It didn't help that the Astros came out of the All-Star break struggling offensively, helping Karstens (8-4) extend his career-best winning streak to five games.

``He's a hard pitcher to face when you're coming out of the break after four days off,' Astros center fielder Michael Bourn said.

Houston starter Brett Myers (3-10) struck out a season-high 11 but gave up three early runs on the way to picking up his fourth loss in as many starts.

``After the third inning, I thought he threw the ball extremely well, a lot like he threw last year,' Astros manager Brad Mills said. ``To see the six strikeouts out of the 11 hitters he faced after the triple in the third inning, that was pretty good. It was nice to see him so aggressive.'

Houston's offense, by contrast, was anything but.

It was the Astros' fifth straight defeat and ninth over the past 10 games. It was Houston's fourth consecutive home loss and 17th over the past 20 games.

The defeat dropped them to 2-8 against the Pirates this season after finishing 11-4 against them in 2010.

The Astros dropped their April 1 season opener at Philadelphia 5-4. Three games later, they dropped to last place in the NL Central standings, where they have remained since.

Pittsburgh entered the game four over .500 at this point of the season for the first time since 1992. By night's end, the Pirates were tied for first place in the Central.

Karstens held the Astros to just one hit - Hunter Pence's single in the second - through the first five innings.

He retired 13 straight after Pence's hit before allowing consecutive singles to pinch-hitter Chris Johnson and Bourn in the sixth. Karstens improved to 3-0 and dropped his ERA to 0.41 in three starts against the Astros this season.

``You don't see it very often that a guy throws 83 pitches for a complete game, and he only had 18, 19 balls,' Mills said of Karstens. ``It was pretty impressive. Everything was working for him. He was getting ahead of guys.'

And he did it at a fast pace, helping to wrap up the game in 2 hours, 20 minutes, which complicated things further for the Astros.

``He was too efficient,' Mills said. ``The guys have done such a good job of lengthening him out, but every time we tried to do that, we were behind 0-2, and it became something that was really tough to get into.

``He wouldn't really give us a chance (to slow him down). He kept pounding the zone.'

Bourn agreed.

``He was coming out (and) getting ahead real early,' he said. ``That's what was good for him. He wasn't falling behind. He was attacking with the fastball.

``When (a pitcher's) attacking, you either take or you swing early. He wasn't missing too much.'

It was Karstens' first shutout since Aug. 6, 2008, at Arizona.

Andrew McCutchen hit a one-out triple out of Bourn's reach in the top of the third inning to drive in two runs for the Pirates, who won their second straight and sixth of their last 10.

``I made a mistake,' Myers said of his pitch to McCutchen. ``I tried to go in and I pulled a little bit over the middle of the plate. They're supposed to hit balls like that. I was hoping (Bourn) could run it down, but it got away from him.'

Alex Presley singled to lead off the game, stole second and scored on a one-out single to right by Neil Walker.

Pence reached third base - the only Astros player to do so - in the seventh on a single by Carlos Lee, but Brett Wallace grounded into a double play to end the inning.

Pinch-runner Xavier Paul scored on a fielding error by Astros second baseman Jeff Keppinger in the eighth to cap the scoring.

NOTES: The Pirates recalled LHP Joe Beimel (left elbow inflammation) from the 15-day DL on Friday. Pittsburgh optioned LHP Daniel Moskos to Triple-A Indianapolis on Thursday to clear a spot on the roster. ... Friday was the 15th time in his career that Myers finished with double-digit strikeouts. ... Houston OF Jason Bourgeois (right quadriceps strain) went 0 for 3 on Friday in his rehabilitation assignment with the Gulf Coast League Astros. He is scheduled to join Double-A Corpus Christi on Saturday.