SAN FRANCISCO -- It was somehow fitting that on Casey McGehee's most memorable night as a San Francisco Giant, he grounded into two double plays.

The league leader in twin killings added to his total Friday night, but not before he belted a grand slam that propelled the Giants to a 6-0 victory over McGehee's former team, the Miami Marlins.

Right-hander Tim Lincecum contributed to his second consecutive shutout, hot-hitting first baseman Brandon Belt had four hits, including a double in a sixth consecutive game, and catcher Buster Posey reached base five straight times and scored three runs as the Giants avenged a 7-2 loss the night before to even the four-game series at one game apiece.

"I can go home and have a good feeling about my four at-bats," McGehee insisted after hitting the ball hard four consecutive times, twice for hits and twice into double plays. "I'm pleased with the part I could control. Where the ball goes after you hit it, you can't control."

McGehee, a third baseman who had been benched for three consecutive games because of an 8-for-56 slump, showed no rust in his first plate appearance of the night in the second inning, crushing a fastball from Marlins right-hander Jarred Cosart into the bleachers in left-center field for his first grand slam since 2010.

The home run was just the second of the season for McGehee, who left the Marlins as a free agent over the winter. The four RBIs were one more than he had totaled in his first 29 games as a Giant.

"I was thinking sacrifice fly," McGehee said of a bases-loaded, one-out situation in a scoreless game in the second inning. "I got a good pitch to hit and put a pretty good swing on it.

"It was an important at-bat for me. I felt like I've hit the ball hard. I'm starting to feel like myself."

McGehee's third career grand slam came after Belt's double helped set the stage. Belt's hit followed a single by Posey and preceded a walk to right fielder Justin Maxwell.

Shortstop Brandon Crawford struck out for the first out, setting up a possible double play to end the inning.

"Casey got that big hit for them," Marlins manager Mike Redmond lamented. "He grounded into two double plays ... just not when we really needed the double play."

The four-run cushion was more than enough for Lincecum and right-handed reliever Yusmeiro Petit, who combined on a three-hitter.

Coming off a 5-0 win over the Los Angeles Angels of Anaheim in which he pitched eight shutout innings, Lincecum (3-2) blanked the Marlins for six before leaving with a 5-0 lead. He gave up all three of the Miami hits and walked three, but struck out a season-high eight.

"Today felt better than most," Lincecum said. "I was pretty erratic at times, but I made pitches when I needed to."

Three such pitches came in the top of the fifth, when he faced Marlins slugger Giancarlo Stanton with the bases loaded and the Giants leading just 4-0. Lincecum struck out Stanton on three pitches to end the threat and retain the shutout.

"That was a big situation," said Lincecum, who thrust his fist into the air after Stanton's final swing and miss. "I was pretty excited about it. It was an emotional setting."

Belt improved to 12-for-22 during his six-game hitting streak by stroking four consecutive hits before striking out in the eighth inning.

Belt has hit a double in six straight games, a streak that's one shy of the Giants' all-time franchise record.

Posey singled twice before walking three consecutive times. He also scored on McGehee's slam, as well as providing the Giants' scoring in the fifth and seventh innings.

Maxwell had two hits and two RBIs, driving in Posey with the last two runs.

In snapping a two-game losing streak, the Giants had 12 hits. They, however, failed to score more than six runs in a 30th consecutive game this season.

Petit, who was credited with his first career save, faced just one over the minimum nine batters in his three-inning, hitless stint. He walked one and struck out two.

Center fielder Marcell Ozuna had a double and a single for the Marlins, who had pelted the Giants with a season-high 17 hits in Thursday's win.

"We couldn't get anything going," Redmond said. "We had one shot and it didn't happen."

Cosart (1-3) lasted only four innings, allowing four runs on six hits. He walked three and struck out two.

NOTES: Giants 3B Casey McGehee grounded into two double plays, his 10th and 11th of the season. ... McGehee batted eighth in the San Francisco lineup. The last Giants No. 8 hitter to hit a grand slam was SS Miguel Tejada in 2011. ... Giants RHP Tim Lincecum had eight strikeouts in the win. He now needs six to catch LHP Carl Hubbell (1,677) for fourth place on the franchise's all-time strikeout list. ... Lincecum's six shutout innings extended his streak to 15 dating back to April 27. ... Marlins 2B Dee Gordon, the major league leader in batting average and hits, did not play because of a sore right leg suffered when he lunged awkwardly for home plate in the ninth inning of Thursday's game. Gordon is expected back in the starting lineup Saturday. ... Before the game, the Marlins activated LF Christian Yelich (strained lower back) from the disabled list and designated INF Reid Brignac for assignment. ... Giants RF Hunter Pence began an injury-rehab stint at Triple-A Sacramento on Friday night.