HOUSTON -- Ryan O'Malley got the wakeup call every Minor League ballplayer dreams of.

O'Malley had been scheduled to pitch out of the bullpen Wednesday for Triple-A Iowa against Round Rock because Wade Miller was going to make a rehab start. Instead, O'Malley hopped in a limo around 6:45 a.m. CT and was driven about 130 miles to Minute Maid Park for his Major League debut. And, best of all, he got to pitch for his favorite team, the Cubs.

"[Iowa trainer Bob Grimes] said, 'Get ready, you've got to catch the car,'" O'Malley said. "I've been smiling since."

The seventh rookie pitcher to start this season for the Cubs, O'Malley won his Major League debut Wednesday, giving up five hits over eight scoreless innings in a 1-0 victory over the Houston Astros. Michael Barrett hit his 14th home run with one out in the sixth inning off Andy Pettitte (11-13) to help O'Malley and the Cubs complete the sweep.

Barrett, the Cubs catcher, had never caught O'Malley before. The southpaw had appeared in a couple of Spring Training games, but that was it. Cubs pitching coach Larry Rothschild gave the young lefty the Astros lineup, said this guy does this, this guy does that -- let's go.

"He told me what he likes to do, and he had a game plan from the start and did a great job," Barrett said of the rookie. "He threw strikes, that's the difference. It didn't look like he was the type of guy who strikes a lot of people out."

He isn't.

"I'm not going to overpower you with a fastball," O'Malley said. "I'm just going to pitch."

The lefty fanned two and walked six, which bothered him.

"That's my strength, not walking guys," he said. "Maybe the umpires have a little different strike zone. I wasn't going to give in; I just battled 'em."

The hardest hit ball was a comebacker by Chris Burke in the third. He also called Barrett off on Jason Lane's popup that deflected off the stadium roof. That was a first for Barrett.

Carlos Zambrano delivered a shaving cream pie to the face while O'Malley was doing a postgame TV interview, and the Cubs players doused him with a celebratory beer shower. Nothing could wipe the smile from his face.

"I grew up a diehard Cubs fan my entire life," said O'Malley, raised in Springfield, Ill. "Springfield's 50-50 Cubs-Cardinals, and I've got some diehard Cardinal fans in my family and I'm sure they're smiling today as well."

O'Malley entered the game with 28-23 record and 3.85 ERA in 167 career Minor League games over five seasons. The 26-year-old southpaw was not drafted, but signed with the Cubs as a free agent on June 7, 2002.

How did the Cubs find him? He was signed by scout Pat Portugal out of the University of Memphis. Portugal had actually gone to see a kid from Tulane, who ended up being a second-round pick.

"After the draft, [Portugal] offered me an opportunity and I'm trying to make the best of it," O'Malley said.

O'Malley was filling in for Wednesday's scheduled starter, Rich Hill, who had to pitch in Tuesday's 18-inning marathon. The Cubs needed a fresh arm and the bullpen needed a break. The lefty became the second rookie to win his big-league debut this season, joining Juan Mateo, who did so Aug. 3 against Arizona. They're the first Cubs to do so since John Koronka won his debut June 1, 2005, at Los Angeles.

He actually went to Memphis as an outfielder and was converted to a pitcher. Hall of Famer Ryne Sandberg is his favorite player, and O'Malley's nickname is familiar to Cub fans -- Ryno.

"I got to meet him in Spring Training," O'Malley said. "It's an awesome road."

This season, O'Malley was 7-7 with a 4.08 ERA in 26 games, including 19 starts, for Iowa. The Cubs' kid pitchers have now started 48 games this season, and are 14-21. It's the most since 2002, when rookie pitchers started 51 games for the Cubs. Before that, the highest total was 57 games in 1967, and 74 in 1966.

He spent the morning drive in the back of the limo calling friends and family with the news. Was he nervous?

"I didn't have time -- it all happened so fast," O'Malley said. "I still don't know what's going on."

"That was sweet," Cubs manager Dusty Baker said. "The young man worked quickly and he had them off-balance all day long. Eight innings in your first outing and your first win, and that's a young man from Illinois. I bet his parents are happy -- I know we are."

It's a dream come true.

"I wouldn't play the game if not for that dream," O'Malley said. "This is the ultimate dream of mine."