Three straight losses proved that little has changed for the Reds, at least in this NL Central matchup.
"We would have liked to have had a better showing here," said Reds slugger Adam Dunn, who went 1-for-4. "But it's not the end of the world. We just couldn't get the big hit at the right time, like we did the series before."
Bagwell homered in the fifth to give Houston a 4-2 lead and Morgan Ensberg followed with a solo shot for the Astros, who won their series-record 11th consecutive game -- eight last season -- against Cincinnati. Houston won 10 straight against their longtime division rival in 2003.
"I don't know what happens," Astros manager Phil Garner said of his club's streak against the Reds. "It's just a strange thing."
After a poor start in an opening day loss to St. Louis, Oswalt (1-1) rebounded with another dominating effort against the Reds. Oswalt limited Cincinnati to two runs on five hits, but walked five and struck out only two.
"I was a little wild ... but I felt I made some good pitches when I had to," Oswalt said. "Call it effectively wild. I was just wild enough that they couldn't concentrate. Sometimes when you're wild it helps you."
He improved to 12-0 in 16 career appearances -- 14 starts -- against the Reds. Only Pedro Martinez (13-0 against Seattle) has won more games against one team without a loss.
"I hope it's not a fluke," Oswalt said. "I hope it keeps going."
Milton, who led the NL with 43 homers allowed in 2004, gave up three Sunday, including a solo shot to Craig Biggio in the first.
Cincinnati's new lefty lasted only 4 1/3 innings, allowing five runs on eight hits with two strikeouts and one walk. Milton dropped to 0-3 in four career starts on short rest.
"I was weak, but my arm felt fine," Milton said. "I may have just hit a wall there in the fifth. I didn't have a lot of gas left ... it just wasn't there today."
The Reds couldn't hold an early lead against Houston -- same as Saturday when the Astros rallied from a 3-0 deficit.
Wily Mo Pena tied the game at 1-all in the second, sending an Oswalt fastball into deep left, a 408-foot shot that bounced off the replica 1860 railroad tracks atop a 58-foot wall.
Dunn added a run-scoring triple off the right-field wall in the fourth, giving the Reds a 2-1 lead.
"They came up with the big hits and we didn't," Reds manager Dave Miley said. "We just couldn't get over the hump."
Biggio went 3-for-4 with a double and the homer. He also stole third base in the seventh, making him the sixth player in league history with 100 career steals of third.
Burke, making his first start in the majors, also finished 3-for-4.
Cincinnati continues its grueling road trip Tuesday with two games against NL defending champ St. Louis. The Astros, meanwhile, head to New York for a three-game series against the 1-5 Mets, starting Monday.
It will be Houston's first time facing Carlos Beltran since he left for the Mets in free agency this offseason.
- Houston swept a series against the Reds for the third straight time.
- Bagwell hit his 448th career homer.
- With three hits Sunday, Biggio passed Jimmie Foxx for 65th place in league history with a total of 2,649. He needs five more hits to tie Ted Williams for 64th.
- The Astros are one of only three clubs to not allow a stolen base this season.
- Biggio's youngest son, Cavan, threw out the first pitch. Cavan turns 10 on Monday.