PITTSBURGH — Pittsburgh Pirates right-hander Jeff Karstens has told his manager he’d be willing to start on only a day’s notice.

Clint Hurdle gave him some extra time. A rainout Tuesday helped even more.

Hours before the Pirates’ game against the Milwaukee Brewers was postponed due to rain Tuesday night, Hurdle announced that Karstens would take Ross Ohlendorf’s spot in the rotation.

“He’s fresh and he’s ready and he’s coming off a large volume of pitches,” Hurdle said.

Ohlendorf left his last start Friday during the third inning due to a strained shoulder, and he was replaced by Karstens. Karstens promptly threw 3 1-3 scoreless innings, allowing the Pirates to stay in a game they ultimately won 4-3 in 14 innings.

That was typical for Karstens, who has served in a variety of roles for Pittsburgh since being acquired in a trade from the New York Yankees in 2008. Karstens made 41 starts over his first 2Z\x seasons with the club, and he’s also made 36 relief appearances ranging from long man to set-up guy.

“I’ve had several conversations with him, and I know he doesn’t have an agenda,” Hurdle said. “Most players have an agenda. He wants to pitch.”

Karstens originally was to pitch the series finale against Milwaukee on Thursday, but the rainout pushed him back into the weekend series in Cincinnati.

The Pirates and Brewers pushed back their starters for the series. That means that Milwaukee’s Shaun Marcum will face Kevin Correia Wednesday instead of Tuesday, and the Randy Wolf-Paul Maholm matchup is bumped back to Thursday.

The Pirates didn’t announce their pitching plan for the weekend, but Karstens, Charlie Morton and James McDonald will be their three starters.

The makeup date for Tuesday’s scheduled game will be announced at a later date.

The Brewers got plenty of good news on the unscheduled day off. Two of their marquee players on the disabled list took significant steps in their return.

Right-hander Zack Greinke and outfielder Corey Hart each worked out in the bowels of a soggy PNC Park, and both came away feeling strong — and having impressed manager Ron Roenicke.

Greinke threw a 25-pitch simulated game in a batting cage Tuesday in his latest step to return from a cracked rib.

Notes: Pirates RHP Evan Meek (right shoulder tightness) will be available Wednesday for the first time in seven days. ... Pirates LHP Joe Beimel threw an inning of relief for Triple-A Indianapolis.