HOUSTON -- Carlos Zambrano put his Opening Day jitters behind him.
"I wasn't thinking that today was Opening Day," Zambrano said. "I was not in a panic, not nervous. I was just in control of myself. I was thinking it was another game, another game of my career, another game for the Chicago Cubs. Just go out there and have fun, perform good."
Zambrano allowed one run and five hits over six-plus innings in his first start against Houston since his no-hitter on Sept. 14 in Milwaukee. That game was played at Miller Park after Hurricane Ike damaged the Houston area.
Cubs manager Lou Piniella said before the game that the 27-year-old Zambrano would get too nervous and excited on Opening Day in years past. But things were different this time around.
"He pitched well, he really did," Piniella said. "The way we drew it up before the ballgame is the way the game played out. It's a good formula. Let's hope it continues to work."
Zambrano (1-0) struck out six and walked three to break an Opening Day winless streak that began on April 4, 2005.
"That Zambrano, he's a superstar pitcher," Houston's Miguel Tejada said. "When they get up two runs like that it puts a lot of pressure on you against a guy like him."
Marmol walked one during a scoreless eighth inning.
Soriano connected on Oswalt's second pitch and Ramirez made it 2-0 with his second-inning homer to the Crawford Boxes in left field.
"Soriano, basically in that leadoff hole, is instant offense," Piniella said. "When he's swinging the bat, and they're going over the fence, and he's getting doubles instead of singles, then he gives us a big spark. When he's focused at home plate, swinging at strikes, he's an offensive machine."
Oswalt (0-1), who extended his franchise record with his seventh consecutive Opening Day start, gave up three runs and seven hits over seven innings. He dropped to 2-3 in openers.
"I felt better later," Oswalt said. "I thought I threw the ball pretty well after the third or fourth inning. Before that I wasn't getting up on the ball."
Houston had runners on first and third in the third inning before Zambrano retired Ivan Rodriguez and Lance Berkman to end the threat. The right-hander retired the next eight batters, striking out five, before walking Berkman with two outs in the sixth.
Newcomer Aaron Heilman replaced Zambrano with no outs and runners on first and second in the seventh. Heilman got Pence to ground into a double play but Michael Bourn drove in Tejada with an infield single. Neal Cotts then got pinch-hitter Jason Michaels to ground out.
Pinch-hitter Micah Hoffpauir had an RBI single in the ninth for Chicago.
The Astros, who added Rodriguez last month in hopes that he'd boost their offensive output at catcher, had an inauspicious debut, going 0-for-4 with a pair of strikeouts.
He was one of several Astros who didn't get a hit Monday.
"I'm not worried about that," manager Cecil Cooper said. "Eventually I know these guys will hit."
Lyle Lovett sang the national anthem. He also sang the anthem at the first game at Minute Maid Park on March 30, 2000. ... Zambrano's fifth consecutive Opening Day start tied a Cubs record. ... Ramirez's home run was the 250th of his career and his 174th as a Cub.