WASHINGTON -- Astros right fielder Hunter Pence left Tuesday's 8-4 loss to the Nationals with discomfort in his right hip flexor and is considered day-to-day.

Pence grounded out to third for the first out in Houston's three-run first inning, and was replaced in right field by Brian Bogusevic in the bottom of the inning.

Pence is hitting .280 with 24 home runs and a career-high 85 RBIs in 145 games. He snapped an 0-for-13 slump with a ninth-inning single in Monday's 8-2 win against the Nationals.

Pence said he's dealt off and on with a hip flexor for some time, but exacerbated the problem area by running too hard to first base on his first-inning grounder.

"I've dealt with it my whole career," he said. It was bugging me a little bit, but I think I pushed a little too hard on that run to first, and that's what got it more than you can play on."

On the way back to the dugout, he knew the hip would prevent him from running hard in the outfield.

"When you tweak something like that, you can't run through it," Pence said. "It's impossible. I knew that I wasn't going to be capable to sprint again. I would have had to jog, and that's not acceptable in the outfield."

Pence expects to miss two or three days, but manager Brad Mills said he would be re-evaluated before Wednesday's third game of the four-game series at Nationals Park. For now, Mills considers Pence day-to-day.

"It might be a couple of days," Mills said. "We'll just have to see how it is. We'll check him in the morning and probably know a little bit more tomorrow."

Bourn might need another game or two

WASHINGTON -- Outfielder Michael Bourn, the National League's leader in stolen bases, was out of the Astros' lineup for a second straight game Tuesday and said it may take him another day or two to recover from a strained right side muscle.

"End of the series, at least," Bourn said when asked about the oblique muscle strain that forced him from Sunday's 4-3 win over the Reds. "I don't know. I can't tell. I've never had one of these injuries. I don't know how they progress."

Bourn, who has 52 stolen bases and has reached base via hit or walk in 27 consecutive games with a plate appearance dating to Aug. 21, hurt himself Sunday after fouling off two pitches against the Reds. He's not concerned by the slow recovery process because he's heard that oblique injuries can be tricky.

"I've heard they can take a little while, so there's nothing I can do about it," Bourn said. "I'm not going to play until I feel like I can go pretty good. Right now, I can't go pretty good."

Bourn said there was no change in his condition from Monday, when the ribcage muscle was too sore to allow him to swing without discomfort.

"He was still pretty sore yesterday," Astros manager Brad Mills said Tuesday. "I haven't had a chance to see him today, but I'm anticipating that being a little tender still."

All of which leaves Mills and Bourn in a holding pattern. Jason Bourgeois started in center field in place of Bourn for a second straight day.

"[I'll] just sit and wait -- and wait until it heals," Bourn said.

Lee remains in Astros' first-base picture

WASHINGTON -- Astros manager Brad Mills continues to be impressed by left fielder-turned-first baseman Carlos Lee's transition to his new position and acknowledged that the team had internal discussions last offseason about playing Lee at first and shifting then-first baseman Lance Berkman to left field.

"That had been considered," Mills said.

Lee made his 12th start at first on Tuesday against Washington -- his most extensive time at the position since five games and four starts for the White Sox in his 1999 rookie season -- and has reached a quick comfort level there.

"He's looked good down there from Day 1. The thing is, because he had come up as an infielder, that definitely has helped him with that transition," Mills said.

Strangely, Lee's name wasn't mentioned as a possible fill-in when a knee injury forced Berkman to miss the start of the season. Mills danced around a question about whether Lee could play full-time at first in 2011.

"What are the percentages? I have no answer for that question," Mills said.

The new position certainly hasn't negatively affected Lee's work at the plate. Lee entered Tuesday with hits in eight straight games, batting .394 with three homers over that span.

Byrdak approaches role an out at a time

WASHINGTON -- Tim Byrdak carried a streak of 12 2/3 scoreless innings into Tuesday's game against the Nationals, and the veteran lefty has been adding to his shutout streak the hard way -- one-third of an inning at a time.

When Byrdak fanned Washington's Adam Dunn with the bases loaded in the seventh inning on Monday's 8-2 victory, it marked the sixth straight appearance that's required him to record only one out. Eleven of his past 12 outings, and 24 of his 60 appearances have followed the same script.

"I try not to think about it," said Byrdak. "Your job is to go out there and get outs, and you don't worry about any other stuff."

Byrdak hasn't allowed a run in 41 of his past 42 outings -- the Reds tagged him for two runs on July 23 -- and has flourished as a situational reliever. But he can still stretch it out when needed.

"It's been a different role this year than last year," Byrdak said. "Last year, I did long stuff, short stuff, a mixture of everything. This year, it's more situational stuff."

He doesn't mind the one-batter-at-a-time philosophy, as long as manager Brad Mills realizes he can go longer if the situation dictates. Byrdak worked a season-high two innings at Chicago on Sept. 7, when the Cubs' lineup he was slated to face had six left-handed hitters in a seven-batter span.

"You don't ever want to get labeled as just a situational guy, because in the long run, it can come back to hurt you," Byrdak said. "If you're known as a guy who can come in and get both lefties and righties out, that's more beneficial to you to be able to go an inning or two."

A starter early in his Minor League career, Byrdak never pitched a shutout. Now he's got the equivalent of one.

"I don't ever recall going a full nine-inning complete game in my [Minor League] career," said Byrdak, who did throw one complete game for Gary of the Independent League in 2003. "A couple [hitters] here and there and I guess I have."

Astros visit soldiers at Walter Reed

WASHINGTON -- A contingent of more than 50 members of the Astros' organization -- including players, coaching staff and front-office staff -- spent several hours Tuesday morning visiting wounded soldiers at the Walter Reed Army Medical Center.

The visit has become an annual affair under the leadership of Astros chairman and CEO Drayton McLane, who accompanies the team to the nation's capital for its yearly road trip.

"It's probably a lot of times a better experience for us than maybe it is for those guys there," said manager Brad Mills. "You get a sense of gratitude for what they have done to help protect our nation, and that's pretty special."

Only one thing surprised Mills in his encounters with the wounded warriors.

"They wish there was some way they could go back. They're soldiers. That's what they do," Mills said.