Jason Lane hit a two-run homer, Oswalt won his fifth consecutive decision and the Houston Astros sent the slumping Los Angeles Dodgers to their ninth loss in 11 games with a 4-1 victory Monday night.
Oswalt (13-6) gave up a run and six hits in eight innings with two walks and three strikeouts. The right-hander hasn't allowed more than one run in any start during his winning streak.
"It feels great, especially when you know you can make a quality pitch when you need it," Oswalt said. "The more you pitch, the more you learn to try to keep the pitch count down, not try to strike out too many guys and get double plays when you can."
Thanks to their ace, the Astros improved to 2-9 against NL West teams on the road.
"You've got to have somebody that puts an end to your bad times and keeps your good times going, and Roy's the guy you can count on to do that all the time," Houston manager Phil Garner said. "He threw strikes, was aggressive and went after them."
Chad Qualls pitched a perfect ninth for his third save in six chances.
Chad Billingsley (7-4) allowed four runs and six hits, struck out seven and walked four in losing his fourth consecutive outing.
"It was a battle," he said. "Just got runners on and my mechanics started rushing and I found myself getting behind hitters more often. When things start going quickly, I start rushing and find myself getting in trouble and just barely missing, instead of just trusting my ability."
The Dodgers opened the four-game series against Houston with their third loss in a row. They have dropped seven consecutive series while falling out of first place in the NL West over the last two weeks.
Juan Pierre was the only Dodger with any success against Oswalt, going 3-for-4.
"He's a bulldog," Pierre said. "We hit a couple balls hard right at guys. When you're struggling as a team and you got a guy like that on the mound, the ball always seems to find their glove."
The Astros extended their lead to 4-0 with three runs in the fifth. Luke Scott had an RBI single, followed by Lane's two-run shot into the left-field pavilion on a 1-1 count from Billingsley.
"I was frustrated with leaving some guys out there my first two at-bats, but I was able to make an adjustment," Lane said. "I feel like I'm having good at-bats and I'm always confident that I can get a big hit, and it's worked out a few times."
The Dodgers avoided the shutout on Rafael Furcal's sacrifice fly in the fifth.
Houston led 1-0 in the fourth on Chris Burke's RBI groundout.
Dodgers third baseman Nomar Garciaparra got ejected for the first time in his 12-year career in the bottom of the inning for arguing a called third strike by umpire Tom Hallion.
"There's a first time for everything," Garciaparra said. "I thought the ball might have fallen off the plate. We argued and had a disagreement. I was respectful to him and he was respectful to me."
Los Angeles manager Grady Little came on the field to talk to Hallion, while first base coach Mariano Duncan wrapped his arms around Garciaparra and attempted to lead him back toward the dugout.
Garciaparra continued shouting and pointed his bat at Hallion while taking a few steps toward the umpire, who then tossed him.
- Pierre stole his 46th base of the season, most by a Dodger since Eric Young swiped 51 in 1999.
- Recently acquired INF Mark Sweeney singled in the fifth, his first base hit with the Dodgers.
- Oswalt's five-game winning streak is his longest since he won nine in a row from last Aug. 23-April 7.
- Oswalt moved into sole possession of third place on the Astros' career win list with No. 111.
- Garciaparra went 4-for-15 on the Dodgers' just completed road trip.