Pedro Alvarez hit a three-run homer and Zach Duke pitched into the seventh inning for the second consecutive start, leading the Pittsburgh Pirates to a 6-4 victory over the Houston Astros on Saturday night.

Duke (8-14) was pulled by manager John Russell after giving up Humberto Quintero's leadoff single in the seventh. The left-hander allowed three runs and seven hits while walking one and striking out three.

Duke tossed 7 1-3 innings in a no-decision against Arizona last Sunday. He had not made it into the seventh in back-to-back starts since pitching seven innings against Atlanta on April 10 and Cincinnati on April 16.

Joel Hanrahan gave up an RBI double to pinch-hitter Brian Bogusevic with two outs in the ninth, then retired Geoff Blum on a grounder for his sixth save.

Alvarez had two hits, including a home run off Bud Norris (9-9). Andrew McCutchen also had two hits and scored twice as Pittsburgh rallied from a 3-0 deficit to win for the sixth time in eight games.

Norris had his three-start winning streak snapped as he was tagged for five runs and seven hits in 4 2-3 innings. Houston had won his previous six starts.

Jose Tabata singled in the go-ahead run off Norris in a two-run fifth that snapped a 3-all tie and put the Pirates ahead for good. The Astros lost their fourth in five games.

McCutchen doubled leading off the fifth and Tabata followed with a single. Tabata moved to second on Neil Walker's single and scored on Ryan Doumit's single to left to make it 5-3.

The Pirates added a run in the eighth when Alvarez scored on a wild pitch by Matt Lindstrom.

Quintero had two hits, including a two-run double in the fourth that gave the Astros a 3-0 lead. Pittsburgh answered with Alvarez's homer, his 13th, in the bottom half. It scored McCutchen, who had singled, and Walker, who had walked.

Houston opened the scoring in the second when Jason Michaels led off with a double and came home on a single by Chris Johnson, who had two hits.

NOTES: Pittsburgh RF John Bowker left the game after the fourth inning with a sore left knee. RHP Jeff Karstens, who has not pitched since a start on Aug. 31, hopes to work in relief during the Pirates' season-ending road trip that begins Monday. ... At 74-81, Houston must win its last seven games to avoid having back-to-back losing seasons for the first time since 1990-91. ... Astros coaches Brad Arnsberg, Dave Clark, Bobby Meacham, Al Pedrique and Jamie Quirk all signed two-year contract extensions. Hitting coach Jeff Bagwell wants to mull over his decision about coming back next season.