Blanton (4-3) allowed six hits and one run, struck out seven and walked one while pitching in a steady light rain throughout. The right-hander continued his solid recent stretch, improving to 3-0 with a 2.10 ERA in his last four starts.
Freddy Galvis had three hits and drove in a pair of runs and Carlos Ruiz went 2 for 4 with an RBI for the Phillies, who have won three of four since manager Charlie Manuel's much-publicized team meeting last Wednesday. Ruiz entered the game leading all major league catchers in average (.330), RBIs (22) and slugging percentage (.588).
Marwin Gonzalez, pinch hitting to lead off the eighth, hit his first major league homer for the Astros' lone run.
Carlos Lee went 3 for 4 for Houston, which has lost six of eight after a season-best five-game winning streak. Lee, who recorded all three hits off Blanton, now is 9 for 18 lifetime against the Philadelphia pitcher.
The Phillies took a 1-0 lead in the fifth inning on Galvis' RBI single to right. Philadelphia was helped in the frame by shortstop Jed Lowrie's fielding error on John Mayberry Jr.'s grounder up the middle, making the run unearned for Houston right-hander Lucas Harrell (2-3). The Phillies could have added to the advantage, but stranded the bases loaded on Juan Pierre's groundout.
Philadelphia went up 3-0 in the sixth on Ruiz's single to left that scored Shane Victorino, who opened the frame with a triple, and Galvis' opposite-field single. Galvis' hit came off Wilton Lopez, who relieved Harrell.
Rather than walk Galvis and load the bases for Blanton, Astros manager Brad Mills elected to pitch to Galvis. And the rookie who is filling in for injured All-Star Chase Utley (knee) at second base, made Houston pay with an opposite-field liner that scored Polanco.
Galvis, batting .231, now has 15 RBIs on just 25 hits.
Harrell left after allowing three runs - two earned - on five hits in 5 2/3 innings, with three strikeouts and two walks.
The Astros nearly got on the board twice against Blanton, with Lee, in the fourth, and Brian Bogusevic, in the sixth, just missing homers down the left-field line.
Altuve followed Gonzalez's homer in the eighth with a single to left, ending the night for Blanton. But Philadelphia relievers Antonio Bastardo and Chad Qualls combined on a scoreless eighth, and Jonathan Papelbon tossed a scoreless ninth, striking out the side, in a non-save situation.
Polanco reached his milestone with a two-run homer, his first off the year, to left field off David Carpenter in the eighth.
Notes: Opponents have one hit in their last 23 at-bats against Bastardo. ... The Phillies' crowd of 43,824 was the 221st regular-season sellout and 237th straight including postseason play. ... The Astros dropped to 32-21 against the Phillies since 2004, still the only NL club with a winning record against Philadelphia during that span. Houston also is the lone NL club with a winning record at Citizens Bank Park, going 16-11 against Philadelphia since the park opened in 2004.