HOUSTON -- Roy Oswalt lasted considerably longer in his start against the Reds on Monday than the last time he tried to come back from a hip injury, and with the help of the bullpen, the right-hander logged his 20th career win against Cincinnati.

The Astros topped the Reds, 5-4, as Oswalt improved to 20-1 over 24 career starts against Houston's division rival. In his first start back since spending two weeks on the disabled list with a strained left hip abductor, Oswalt threw a modest 74 pitches over five innings.

That was a vast improvement over his prior outing, which lasted exactly one inning and 17 pitches against the Nationals on July 11. Oswalt, still dealing with remnants of the hip strain, admitted he came back too quickly to make that start in Washington.

This time, Oswalt had more than two weeks to recover, and apparently, rest and relaxation was the best medicine.

"I wouldn't say I was concerned," Oswalt said. "The last time I went out there, I didn't feel anything, and then when I started going hard, it [hurt]. This time, I had a little more rest. I was hoping it was going to be enough. I felt great through the whole game. I never felt anything."

A beaming manager Cecil Cooper opened his postgame session with the media with two words: "He's back."

"That brings a smile to my face," Cooper said. "He's back, he's feeling good and I just thought five [innings] was good enough. He threw quality strikes and had his fastball."

Oswalt worked out of trouble in the second, logging three strikeouts after yielding a leadoff double to Brandon Phillips and a base hit to Adam Dunn.

Oswalt didn't get so lucky in the third, however. After yielding hits to Jay Bruce and Ken Griffey Jr., he walked Phillips to load the bases, and Dunn emptied them by sending a first-pitch fastball over the wall in left-center. The grand slam was Dunn's 30th home run of the season, and it put the Reds ahead, 4-3.

The lead was short-lived. In the same inning, Geoff Blum answered with a two-run shot off Johnny Cueto (7-10), putting the Astros ahead by a run.

"For the team, it's big answering back," said Blum, who said he detected a mechanical flaw in his swing a week ago after reviewing tape of prior at-bats. "Other than that one pitch, Roy pitched a great game. He's back and he's healthy, so that's a huge key for us. Being able to come back and be in a situation like that, it's a good feeling to put the team ahead and win."

Reds catcher Paul Bako categorized Cueto's pitch to Blum as "probably the worst changeup he's thrown in quite some time."

"Unfortunately, Blum didn't miss it," Bako said. "Johnny actually threw it so high, I assumed Blum would pop it up. It's one of those I wish we had back. Blum is such a good fastball hitter. We definitely tried throwing him some offspeed pitches. Johnny just made a mistake up. He seemed almost out of the zone with it."

Oswalt's exit after five innings was a reasonable ceiling, considering it was his first extended start in nearly a month.

"He probably just got a little winded there in the fifth," Cooper said. "We went and talked to him afterwards, and he was a little bit out of gas."

Said Oswalt: "I wasn't physically tired, but my legs gave out on me more than anything, just [from] not being on the mound [in so long]. The first two, three innings, I wasn't going all out, trying to get into a rhythm to where I could maybe push myself late in the game, and then after I gave up the home run, I got a little irritated at myself and I started throwing a little better after that in the fourth and fifth."

After Oswalt's departure, the bullpen finished the job. Tim Byrdak, Geoff Geary, Wesley Wright and Jose Valverde held the Reds scoreless to preserve Oswalt's win, which evened the right-hander's record at 8-8. Valverde recorded his 29th save.

"The bullpen did a great job coming in for four innings and keeping it exactly where it was," Oswalt said. "They've been doing a great job lately, keeping it close. We've been getting the lead early, and they've been shutting the door for us."

The Astros (49-56) have won all three meetings with the Reds (50-57) this season, and one win in the next two days would give the Astros wins in four of their past five series.

"We're not panicking anymore," Blum said. "Earlier on, when we got guys on base, we started swinging at pitches we probably shouldn't have. Now we're working some counts and getting things to happen. We're good hitters -- it just so happens that we're clicking right now."