PITTSBURGH -- Chris Narveson's pitching is fine so long as his fingers don't get in the way.

Narveson pitched shutout ball into the sixth inning and knocked in two runs after coming off the disabled list to lead the streaking Milwaukee Brewers to an 8-1 victory over the Pittsburgh Pirates in the opening game of a doubleheader Monday.

The left-hander gave up five hits, walked one and struck out three before being forced to leave with one out in the sixth after the nail on his left middle finger started to tear.

It's the second finger-related injury Narveson has sustained this month. He lacerated his left thumb while repairing his glove two weeks ago, sending him to the 15-day DL.

The nail shouldn't be as troublesome, though he took a good ribbing from his teammates.

"(Randy Wolf) said he was going to send me to a manicurist," Narveson said.

Ryan Braun hit his 25th homer for the Brewers, who have won 19 of 22 to open a comfortable lead in the NL Central over second-place St. Louis. Milwaukee also won its 13th straight against the fading Pirates.

Pittsburgh, in first place five weeks ago, fell 16½ games out.

Pirates starter Jeff Karstens (9-7) allowed two runs and six hits in seven innings, walking one and striking out five. But he couldn't find a way to end the Pirates' misery against Milwaukee.

"They're just on a big roll," he said. "I really can't describe it. It's one of those things where we've got to be better than we are."

Nobody's better than the Brewers these days. Milwaukee took another step toward its first division title since 1982 by continuing its dominance of Pittsburgh.

The Brewers haven't lost to the Pirates since July 21, 2010, and have outscored them 51-16 this year.

"I think everybody just keeps pushing no matter how many runs or what the situation or score is," Narveson said.

Narveson's trip to the DL might have been more embarrassing than painful, and once back on the hill he had no issues with the Pirates, who are 8-23 since July 19.

Narveson (9-6) also made a contribution with his bat, giving Milwaukee the lead in the fourth.

Karstens intentionally walked Craig Counsell to load the bases with two outs. Narveson fell behind 1-2 before lacing a curveball to right for a two-run single.

"It was probably too good a pitch for him to take," Karstens said. "I've got to make better pitches than that in that situation."

Narveson figured he knew what was coming when Karstens got ahead in the count.

"I didn't really sit soft but I knew he might come in there with the breaking ball and I was able to stay back on it long enough to get it down the line," he said.

Narveson cruised into the sixth before grimacing after his nail bent awkwardly while he was pitching to Steve Pearce. Though he wanted to stay in after throwing just 85 pitches, Narveson didn't think it was worth the risk.

"I knew if I threw one pitch and it ended it up catching it good and pulling it back or pulling it off, I knew I'd be in big trouble," he said. "I figured, I think we caught it and it should be good."

Narveson gave way to Kameron Loe, and Milwaukee's bullpen limited the Pirates to one run over the final 3 2/3 innings.

Ryan Ludwick hit his 12th homer of the season -- and first since being acquired by the Pirates just before the trade deadline -- while Jose Tabata had three hits for Pittsburgh.

It wasn't nearly enough to cool off the Brewers.

"It's been one of those things where they're playing really, really good baseball right now," Karstens said. "We had them where we wanted them for a little while, we just weren't able to come up with a win tonight."

Game notes
Milwaukee OF Carlos Gomez will take batting practice Tuesday for the first time since fracturing his left clavicle while making a diving catch in Arizona on July 20. ... Milwaukee 2B Rickie Weeks ran on a treadmill as he continues to recover from a severely sprained ankle. ... Pittsburgh catcher Mike McKenry moved to third base in the ninth inning, the first time in his career he's been on the field but not behind the plate.