CINCINNATI -- For Edgar Renteria, the win was the important part. The fact that his game-ending hit came against his former team was just an added bonus.
Jay Bruce started the decisive rally with a leadoff walk on a 3-2 pitch from Brian Wilson (6-3). Miguel Cairo flied out, but reliever Jose Arredondo -- making his first career plate appearance -- chopped a single down the left-field line.
Bruce moved to second on Arredondo's hit and Renteria, the World Series MVP for the Giants last season, lined a soft single down the right-field line to snap the Reds' four-game losing streak.
"It's always special because they're great guys," Renteria said of the Giants. "No matter who we play right now, we have to concentrate on winning ballgames. We were lucky to win that one."
Arredondo's last plate appearance was in 2004 in the Arizona rookie league. The Los Angeles Angels then converted him from a shortstop to a pitcher.
The Reds intended for him to lay down a bunt to advance Bruce but took it off after his first attempt.
"He didn't look too good bunting," manager Dusty Baker said.
"I was really, really happy when I saw the ball in the outfield," said Arredondo, who was surprised Baker took the bunt off. "I stepped out and asked to be sure."
Arredondo (2-3) pitched a perfect 13th.
Newly acquired Carlos Beltran, who went 0-for-4 in his Giants debut on Thursday, had an RBI single in the first for his first hit with San Francisco.
Cincinnati responded with two runs in the bottom half and another in the second. Drew Stubbs singled and scored in the first before driving in Paul Janish with a grounder in the second to make it 3-1.
"Our bullpen is extremely tired but they gutted it out tonight," Baker said. "It could have been a big downer but these guys kept fighting and fighting. Willis went deep in the ballgame but it didn't work. We still had to use guys I wanted to stay away from."
Willis has gotten at least one hit in each of his four starts since being called up from Triple-A Louisville on July 10. ... Left-hander Barry Zito will start Sunday for the Giants. ... Giants left-hander Jonathan Sanchez, on the disabled list since June 25 with left biceps tendinitis, will be activated in time to start Aug. 5 against the Philadelphia Phillies, manager Bruce Bochy said, adding that Sanchez might make one more rehab appearance before then. ... Reds second baseman Brandon Phillips hit a sacrifice fly in the first to give him 500 career RBIs. ... Reds shortstop Zack Cozart, on the disabled list with a hyperextended left elbow, took some swings before the game for the first time since he was injured on July 23.