CINCINNATI -- Giants left-hander Jeremy Affeldt, who has pitched just once since injuring his left hamstring on May 23, was available to pitch in Monday night's series opener against Cincinnati.
"He feels pretty good," said Giants manager Bruce Bochy.
Affeldt's return comes at an opportune time for the Giants. Two of the Reds' top run-producers -- first baseman Joey Votto and outfielder Jay Bruce -- struggle against lefties. Votto is hitting .267 and Bruce .222.
Affeldt, the Giants' top setup man prior to the injury, is 2-3 with two saves in 18 appearances.
Posey gets starting nod at catcher
CINCINNATI -- Giants rookie catcher Buster Posey made his season debut as a starter behind the plate Monday night against the Reds.
Posey, considered among the top catching prospects in the Minor Leagues prior to his being recalled from Triple-A, had made eight previous starts this season, all at first base. He entered Monday batting .433 with four doubles and four RBIs.
"Catcher is my primary position, so I'm excited to get back there," Posey said. "I enjoy catching, working with the pitchers. When I'm at first, sometimes I'll try to think along to what's going on, pitch to pitch."
Giants manager Bruce Bochy said the decision to catch Posey on Monday night was more a matter of timing than an indication that an organizational shift was underway.
Bochy said veteran backstop Bengie Molina, who's been nursing a sore left elbow after being struck by a foul tip a week ago, was in need of a day off. Molina is mired in a 4-for-52 slump.
"It was a good day to give him off," said Bochy.
Posey caught left-hander Barry Zito, who made his 12th start for the Giants. Posey caught Zito twice in his four starts behind the plate last season.
"We'll try to get on the same page," said Posey. "I've been around him enough now that he knows I'm working for him and we should be fine."
Posey said his primary concern Monday night would be how his body will respond to the rigors of catching.
"I'm not worried about tomorrow as much as how I'll feel in the fifth or sixth inning," he said.
Molina reluctantly given night off
CINCINNATI -- Like most players who are struggling, Giants catcher Bengie Molina would rather not take a day off. But the 35-year old veteran, who's mired in a 4-for-52 slump, was on the bench Monday night as rookie Buster Posey made his season debut as a starter behind the plate.
"When you have a day off, it puts more stress in your mind," Molina said. "You just sit and think about what you can do to get out of [the slump]. I don't feel like I'm in a slump. I feel like I'm having great at-bats. I'm hitting the ball hard."
Molina had just four RBIs in his past 38 games after driving in 80 runs last year.
Giants manager Bruce Bochy felt Monday night was a good time to rest Molina and get Posey a start at his natural position.
"He's a little banged up," said Bochy of Molina. "These are decisions that are taken away from the players."
Bochy indicated that Monday's start should not signal the beginning of the Posey Era behind the plate. Molina is preparing for that day and said he would not be a distraction should the club decide to give Posey, long considered the Giants' top catching prospect, the full-time job.
"I respect Bochy and the organization," he said. "I'm not the GM. I consider myself just another player. If they decide to go that direction, what am I going to say? I just have to keep working hard and playing the game the right way. Everything will be all right."
DeRosa to continue Triple-A rehab stint
CINCINNATI -- Giants outfielder Mark DeRosa, who's been on the disabled list since May 17 with left wrist neuritis, will remain on rehab at Triple-A Fresno, for now.
It's not yet determined when DeRosa could rejoin the club, although it's possible he could return as early as Friday when the Giants begin a six-game homestand against the A's at AT&T Park.
"We're not sure yet," said Giants manager Bruce Bochy. "We'll need to re-evaluate it."
Prior to the injury, DeRosa batted .194 in 26 games, including four starts at second base. He's on the DL retroactive to May 9.
Jeff Wallner is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.