HOUSTON -- If the Reds manage to stay in contention late into the season, this was the kind of day that could be regarded as one of the key reasons.

In a game against the Astros that was tied four times, Ryan Freel put Cincinnati up for good with a two-run home run in the top of the 11th leading to a 6-4 victory Sunday.

The Reds earned a series sweep at Houston for the first time since June 24-27, 1999, when baseball was still being played at the Astrodome.

"Our guys kept grinding and won the ballgame," Reds manager Jerry Narron said.

With pinch-hitter David Ross on base after a walk, Freel pulled a 2-2 pitch from reliever Russ Springer into the left-field seats for the game-winner. It gave him the first multihomer game of his career -- the utility player also hit a third-inning homer off Houston starter Fernando Nieve.

"I hit [two] when I was on a rehab assignment at Dunedin [Fla.]," Freel said. "It was many years ago -- feels like it was back in Vietnam, a long time ago."

It was a 3-3 game when Freel walked leading off the top of the 10th against Dan Wheeler. Felipe Lopez fouled off two sacrifice-bunt attempts before slicing a double into the left-field corner. Freel scored the go-ahead run from first base standing up.

Todd Coffey (3-0) was one out from securing the save, but he was unable to shut the door. Craig Biggio slugged a double off the high left-field wall, just missing a homer. Chris Burke followed with an RBI double to left field.

It wasn't the first time the Reds were unable to hold a lead against Burke. It was 3-2 in the bottom of the eighth when Burke's flare to short right field off David Weathers dropped in for a game-tying RBI single that scored Mike Lamb.

Houston's scheduled starter, Roy Oswalt, was a last-minute scratch from the game because of back spasms, prompting a 15-minute delay to the start of the game. It was a break for the Reds -- Oswalt is 15-1 lifetime against them.

"I think that was probably one of the key situations in this game," said Freel, who was in the starting lineup at second base because he was one of the few Reds with decent numbers versus Oswalt.

"Roy Oswalt is 15-1 against us and pretty much lights out when he pitches against us," Freel said. "I was happy he got scratched and could face somebody else. Roy Oswalt is a great pitcher. Keeping him off the mound is a good thing. The other guy pitched a great game."

It turned out Freel had some success against Springer, too. He had one homer in three previous at-bats.

"It's not easy hitting home runs, for me especially," said Freel, who has 14 career homers since 2001 and three this season. "It seemed like the last one I hit off of [Springer] was pretty much the same pitch. It was belt-high, a little bit, and he left it up a little bit down the middle of the plate, or three-quarters in. I was able to put some good wood on it."

"I think it shows, especially after starting 0-2 on the road trip, to come back and win four straight is outstanding. It shows the heart these guys have."
-- Reds manager
Jerry Narron

Nieve stepped in on short notice and allowed two earned runs and five hits over five innings. With one out in the fourth of a 1-1 game, Austin Kearns took a first pitch from Nieve the other way for his first homer of the game. Kearns added a second long ball when he connected for a two-out homer to left field in the sixth off reliever Trever Miller.

Elizardo Ramirez pitched six innings for Cincinnati and allowed two runs and three hits with two walks and four strikeouts. Ramirez escaped a bases-loaded jam in the fifth when center fielder Ken Griffey made a long run and a fully-extended diving catch on a Biggio drive to the left-center-field gap. A run scored on the play, giving Biggio a sacrifice fly.

Esteban Yan pitched the bottom of the 11th to secure his first save since Sept. 28, 2004, when he was with Detroit.

After beginning the 10-day, nine-game road trip 0-2, the Reds have won four straight games. The second-place club remained three games behind the first-place Cardinals. Cincinnati will begin a three-game series at St. Louis on Monday night.

"I think it shows, especially after starting 0-2 on the road trip, to come back and win four straight is outstanding," Narron said. "It shows the heart these guys have. I don't think anyone's going to quit over the next couple of months."