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DENVER -- The Colorado Rockies escaped with a win on Ian Stewart's tiebreaking homer in the eighth inning.

Now, they're hoping to avoid a bigger loss -- Troy Tulowitzki.

The NL wild card-leading Rockies rallied for a 4-3 win over the Cincinnati Reds on Monday despite losing their smooth-fielding shortstop.

Tulowitzki left the game in the seventh with a strained lower back after hitting a game-tying single. He's listed as day to day.

"I'm not sure what happened. I took a swing and I felt a little something and felt like I was a little locked up," Tulowitzki said. "I'm a little sore right now and tight. Maybe I'll wake up and feel good to go [Tuesday]."

Tulowitzki tried to convince manager Jim Tracy that he could remain in the game. He nearly succeeded too, until Tracy saw him jog down the first-base line to test his back and favoring it.

Tracy decided to insert Omar Quintanilla, not wanting to take a risk.

"You can't lose this guy for an extended period of time," Tracy said.

The Rockies ended Cincinnati's seven-game winning streak and maintained their two-game cushion over the San Francisco Giants, who kept pace by beating San Diego on Monday.

Stewart delivered the big blow, hitting a solo shot off reliever Carlos Fisher (1-1) for his 23rd homer of the season. Fisher, who was called up Monday from Single-A Sarasota, said he threw a two-seam fastball that stayed over the heart of the plate.

"I let the team down," Fisher said.

The homer was a measure of revenge for Stewart, who struck out earlier this season against Fisher in Cincinnati.

"I put a pretty good swing on it," Stewart said.

That was the first time all day. Stewart struck out in three previous trips to the plate.

Rafael Betancourt (2-1) earned the win with a perfect eighth, while Franklin Morales, filling in for the injured Huston Street, pitched out of a jam to pick up his fourth save in five chances.

Morales, however, certainly didn't make things easy.

The Reds had two on and none out in the ninth, but Morales got Jonny Gomes to fly out and then Scott Rolen was thrown out on the back end of a double-steal attempt.

The Rockies were ready for just such a scenario.

"I don't want to sit in my dugout and be surprised," Tracy said. "I want to be prepared. We had a plan of attack."

That blueprint included throwing behind the lead runner, not going after the speedy Brandon Phillips, who was trying to steal third.

Still, it took a sensational scoop by Clint Barmes to pluck Chris Iannetta's throw from the dirt and tag out Rolen.

"There wasn't a steal sign," Reds manager Baker said. "[Phillips] has a green light. [Rolen] had a big lead and when he saw Brandon run ... they made a good play. That was a key play because we had Morales on the ropes."

Yet Morales wiggled out of trouble, striking out Darnell McDonald to end the game.

Ubaldo Jimenez went six innings in the no-decision, marking the 25th straight start he's gone at least six. His three runs allowed, though, were the most since July 27 against the Mets in New York.

After the game, the flamethrower said he tweaked his left hamstring running the bases and that it affected his fastball. So Jimenez went with a steady diet of breaking pitches.

Jimenez said he doesn't expect to miss his next start.

"No, no, no," he said. "I'll get better."

The Rockies were thrown out twice at home plate Monday, once when Brad Hawpe tried to score from third on a pitch that got away from catcher Corky Miller and again when Carlos Gonzalez tried to score from first on Todd Helton's RBI single.

No matter, Stewart's blast made up for the baserunning mistakes.

"It's obviously a great game to win, a great game to come back to win," Tracy said.

Game notes

Baker said before the game he had no update on the status of RHP Micah Owings, who left the game Sunday after being hit in the helmet by Atlanta pitcher Kenshin Kawakami. ... Gomes hit a two-run homer in the fourth, his 18th of the season. ... Reds RHP Homer Bailey gave up one run and five hits in 5 2/3 innings.