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05/12/12 7:45 PM ET

Lopez a vital cog in Astros' bullpen

PITTSBURGH -- While closer Brett Myers, who has converted his first nine save chances this year, has gotten most of the credit for the success of the Astros' bullpen, setup man Wilton Lopez is off to a terrific start this season, too.

Lopez entered Saturday with a 3-0 record and a 1.83 ERA and hadn't issued a walk in 19 2/3 innings pitched this season, while striking out 14 batters. He's thrown more innings than any other pitcher in the Major Leagues without issuing a walk.

"He's thrown the ball extremely well and he's back throwing exactly how he did in 2010, when he came up and really burst onto the scene and threw the ball real well," Astros manager Brad Mills said. "He's just doing a great job, and when we can rely on a guy to come in and do that type of job, that's pretty impressive."

Lopez, who has stranded seven of eight inherited runners this season, walked just five batters in 67 innings in 2010, making him the only player in the Majors to walk five or fewer hitters while pitching more than 50 innings. Only four pitchers have done that since 1959.

Last year, he walked 18 batters in 71 innings, while going 2-6 with a 2.79 ERA.

Slumping Martinez slated to play on Sunday

PITTSBURGH -- Astros left fielder J.D. Martinez, who was out of the lineup for the third consecutive game on Saturday, will return to the lineup for Sunday's series finale against the Pirates, according to manager Brad Mills. Martinez has been given some time off while he's in a 1-for-31 slump.

"I plan on getting him in there [on Sunday]," Mills said. "I thought he looked good in early batting practice and regular batting practice [on Friday]. Just talking to him on the bench, he seems to be in a good place. I think he's OK. It's not a discipline thing at all. It's for him to take a breath a little bit. That's all."

Martinez, who's hitless in his last 21 at-bats, is champing at the bit to get back on the field.

"I've been itching the last two days to get out there," he said. "I just feel weird. I don't know what to do with myself when I'm sitting out. I'm ready to get back in there, getting that itch to get going and start hitting again."

Martinez has been doing extra work on the field and in the cage, but he says his problems are probably more between his ears.

"I feel like it's just in my head," Martinez said. "That's why Mills is giving me a couple of days, just to clear my mind."

Worth noting

• Mills has yet to announce who will start Tuesday's game against the Phillies in Philadelphia. But all signs point toward Jordan Lyles, who is 5-0 for Triple-A Oklahoma City and last started on Thursday.

Brian McTaggart is reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.