One of the few true leadoff hitters in the National League, Bourn set a career-high in stolen bases with 46 this season, getting on base more than he has in past. His on-base percentage is the most improved in the Major Leagues, jumping 78 points to .366 this season from .288 in 2008.
"The big key for Michael is when he gets on base he creates havoc and difficulties for the opposition," Cooper said. "When he's on base we're a much better team. Let's face it, we are. He creates those situations where he steals a base or puts pressure on the defense and the pitcher. That makes them deal with the guys coming up behind him."
Bourn recorded his eighth multi-steal game of the season on Wednesday. In games in which Bourn has swiped more than one base, Houston has posted a 6-2 record.
The speedy outfielder is four stolen bases away from becoming the sixth player in Astros history to reach 50 steals. He would be the first Houston player to reach the mark since Craig Biggo in 1998. If he continues his pace, the 26-year-old has a realistic shot at breaking the Astros' single-season stolen base record of 65, set by Gerald Young in 1988.
"Michael is a good basestealer. He has great speed and reads pitchers pretty well," Cooper said. "He works at his craft and has a great burst. After the first two or three steps, he's at full speed. I don't know if he has world-class speed, but he's pretty dog-gone fast."
His speed hasn't just benefited Houston offensively, its helped the club out just as much in the field.
Playing in one of the more spacious center fields in the Majors, there isn't a ball hit in the air that his teammates and coaches think he can't get to.
"His defense continues to shine, and he just keeps getting better," Cooper said. "He's getting great jumps and breaks, and he's just a phenomenal defensive player."
HOU: RHP Roy Oswalt (6-4, 4.01 ERA)
Oswalt received his career-high 14th no-decision after allowing eight hits and five runs in six innings on Sunday against the Brewers in Milwaukee. He gave up a two-run homer to Ryan Braun in the first and another two-run homer to Prince Fielder.
ARI: RHP Yusmeiro Petit (2-7, 6.47 ERA)
Petit showcased his capabilities when he nearly no-hit the Pirates on Aug. 4. But that phenomenal start -- when he allowed just one hit and no runs in eight innings -- is looking more like an anomaly, at least at this stage in the 24-year-old's career. In two outings since, Petit has allowed 10 earned runs, 18 hits and four home runs in just eight innings. His 6.47 ERA is highest in the National League among pitchers who have thrown at least 60 innings.
Carlos Lee hit his 21st home run of the season Thursday night. He has hit 20-plus home runs in nine straight seasons and is on pace to hit .300 with 20-plus home runs and 100-plus RBIs for the third consecutive season. Jeff Bagwell (1998-2000) and Moises Alou (1998, 2000-01) are the only other two Astros players to accomplish that feat.
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Saturday: Astros (Brian Moehler, 7-9, 5.40) vs. Diamondbacks (Max Scherzer, 7-7, 4.00), 6:05 p.m. CT
Sunday: Astros (Bud Norris, 3-1, 4.05) vs. Diamondbacks (Jon Garland, 6-11, 4.42), 1:05 p.m. CT