CINCINNATI -- While deciphering possible clues to the Astros' offensive woes through four games, one item on the stat sheet stood out -- five.

The Astros drew just five walks in the first four games, two by Michael Bourn. By comparison their opponents had 15 walks with an on-base percentage of .405.

"Everybody can play GM when you look at a stat sheet," said first baseman Brett Wallace. "I think the whole on-base percentage thing is kind of skewed."

Astros manager Brad Mills continues to stress quality at-bats to his hitters, and the message is beginning to pay off. In the first inning on Wednesday, the Astros drew three walks, including one with the bases loaded by Wallace leading them to a four-run inning.

Wallace said Astros hitters want to be more patient, but not if it means sacrificing aggressiveness.

"You definitely want to stick to a gameplan," he said. "But if I'm looking for a certain pitch ... I don't want to take it just to be selective. Once balls start falling you'll see the on-base percentage go up."

Bourn exits game with tightness in groin

CINCINNATI -- Astros center fielder Michael Bourn left Wednesday night's game against the Reds with tightness in his left groin. He was replaced in center by Jason Bourgeois in the seventh inning.

"I don't remember doing it at all," Bourn said after Houston's 12-4 loss. "I've felt it before, but it wasn't major. It might just be from the cold weather, not being acclimated to it."

Bourn, who went 1-for-3 with a double and a run scored prior to exiting the game, said he felt discomfort chasing down a double by Joey Votto in the sixth inning.

Bourn received treatment after the game and said he would be evaluated again on Thursday morning to determine his status for the finale of the three-game series.

"I'll see how it feels in the morning and if I can go tomorrow," Bourn said.

Astros confident bats close to breaking out

CINCINNATI -- The Astros hit several balls hard during Tuesday night's loss to the Reds at Great American Ball Park, but it was all for naught in an 8-2 defeat.

First baseman Brett Wallace believes it's just a matter of time before the offense begins to click. But the level of frustration is increasing with each game, and loss.

"It's early in the season, we understand that," Wallace said. "We've put the ball in play hard. We're just going to keep chipping at it. Eventually we'll break through."

The Astros came into Wednesday hitting .215 with two home runs and a .257 on-base percentage. On Tuesday they hit three balls to the warning track and were the victim of fine defensive plays on a couple more occasions.

Astros manager Brad Mills isn't pushing any panic buttons after just four games, but he's hoping things turn around quickly.

"There's no doubt the frustration begins to mount," Mills said.

Mills eager to get relievers work in their roles

CINCINNATI -- Astros manager Brad Mills is looking forward to using his relievers within their roles rather than in mop-up duty with the score out of hand.

"It's the third game in a row that our starters haven't gone deep," Mills said. "We have to get these guys in their roles. Let's utilize them like they're here for. Three games in a row that we've had to just get them innings."

One positive on Tuesday was four relievers combining to allow just one run on three hits in four innings with no walks and three strikeouts.

Most important was getting Brandon Lyon back on the mound after his rough outing on Opening Day in Philadelphia. Lyon pitched a perfect eighth inning with a strikeout on Tuesday.

"The big thing was for Brandon, to get him back in there," Mills said. "He was able to move the ball around the strike zone with all of his pitches."

Defensive shift for Wallace surprises Astros

CINCINNATI -- Astros manager Brad Mills was surprised to see Cincinnati put on a shift against left-handed-hitting first baseman Brett Wallace during Tuesday night's game.

The Red shifted the infield to pull and the outfield more to the left. It seemed to be a drastic maneuver considering Wallace has just 159 big league at-bats and a relatively limited scouting report.

"One thing that crossed our mind was ... he went to school at Arizona State with [Reds starting pitcher] Mike Leake," Mills said. "They played together for two years."

Wallace, who was a teammate of Leake's in 2007 and '08 at ASU, went 1-for-4 on Tuesday, twice flying out to a perfectly positioned Reds center fielder Drew Stubbs.

"The sample size on [Wallace] at the Major League level is tiny," said Mills. "The only thing I could think of is perhaps Mike talked to them about it."

Worth noting

Astros second baseman Matt Downs made his season debut in Tuesday night's loss. He entered the game via a double-switch in the bottom of the sixth inning, going 0-for-1 with a strikeout. Downs was inserted into the game after Bill Hall tweaked his ankle rounding the bases. Hall's injury was not serious.

• Alberto Arias felt good Wednesday, one day after a successful 60-pitch throwing session. He is expected to have a shorter throwing session on Thursday. "We're going to have to go real slow with him, and try to stay away from any setbacks," Astros manager Brad Mills said.