"I would say I'm lucky," he joked.
Renteria hit a grand slam off the 2007 NL Cy Young Award winner and matched his career high with five RBIs, leading the San Francisco Giants to an 8-3 victory over the San Diego Padres on Tuesday night.
Renteria connected in the fourth for his first homer with the Giants, who have won three of four. It was his seventh career grand slam and the first allowed by Peavy in his seven-year career.
"Peavy's one of the best pitchers in the game and I have a lot of respect for him," Renteria said. "It was nice for me and for the team, especially because we won the game."
Renteria was batting just .200 through the first two weeks, leading to some early criticism for the shortstop's $18.5 million, two-year deal with the Giants in the offseason.
But Renteria added to his history of success with Peavy, collecting three more hits off the San Diego ace to raise his career average to .455 against the right-hander.
"He picked a good time for it," manager Bruce Bochy said. "We went against a tough pitcher and had some good at-bats. [Renteria] had a great game for us."
The Giants hadn't done much offensively during their current homestand before breaking out against the Padres. San Francisco had scored just four runs in its previous three games and was shut out by Arizona's Doug Davis.
San Francisco's run total was its second highest of the season. The Giants entered as the second-lowest scoring team in the majors behind Houston.
Renteria scored the Giants' first run on a double-play grounder in the third then hit the first pitch he saw from Peavy in the fourth deep into the left-field stands to make it 5-2. The home run was just the sixth of the season for the Giants, lowest in the NL and second-fewest in the majors behind Oakland.
"I felt good today and I saw the ball good," Renteria said. "It's the first time I've seen the ball like that. Hopefully I can see it like that every time."
Peavy, who struck out 10 and came within two outs of a complete game in a 6-3 win over the Giants on April 11, allowed six runs and seven hits in six innings.
"I know what I have to do to get [Renteria] out but you have to execute," Peavy said. "If you don't execute he's going to make you pay. I tried to throw a cutter that would break out of the zone a little bit and get him to chase. It didn't cut and became an 80 mph fastball over the plate. He did exactly what he's supposed to do."
Matt Cain (2-0) beat San Diego for the first time since 2006 and improved to 2-0 for the first time in his career. The right-hander, who didn't get his first win last year until April 23, scattered nine hits over six innings, yielding just two runs.
"They did get some hits but he didn't put guys on base to add on to any rallies and limited the damage," Bochy said. "Matt really kept his poise out there and threw strikes."
Peavy (2-2) took a step backward after two solid starts and couldn't recover after Renteria's grand slam.
It was the first grand slam allowed by Peavy in 1,284 1/3 innings, the second-longest active streak in the majors, according to Elias Sports Bureau. Houston Astros right-hander Brian Moehler has the longest active streak with 1,360 innings.
Brian Giles singled in a run in the first and Kevin Kouzmanoff added an RBI double in the fourth to give San Diego a 2-1 lead. Chase Headley tried to score on Kouzmanoff's hit and was tagged out at the plate by Bengie Molina.
"We got a bunch of singles and Kouz gets a big hit with the ball in the gap and the inning looks like it has the making of a few runs," manager Bud Black said. "We never got the knockout blow. That was unfortunate for us."
Renteria also singled in Travis Ishikawa in the sixth, giving him five RBIs in a game for the eighth time in his career. Ishikawa had two hits, two RBIs and scored twice.
San Francisco optioned LHP Alex Hinshaw to Triple-A Fresno and recalled C Steve Holm after the game. ... San Diego acquired utility INF Chris Burke from Seattle only a few weeks after the Mariners acquired Burke from the Padres. Seattle received cash for returning Burke to San Diego. ... Padres SS Everth Cabrera underwent surgery to repair the broken bone on his left hand and is expected to be out six to eight weeks. Cabrera will wear a splint for five days and begin therapy next week. ... Boxer Manny Pacquiao threw out the ceremonial first pitch as part of the Giants' Filipino-American Heritage celebration. Pacquiao is scheduled to fight Ricky Hatton for Hatton's IBO junior welterweight title in Las Vegas on May 2.