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NEW YORK -- At times, Tim Lincecum was every bit an ace. At others, all over the place.

"I didn't feel like I had a good rhythm," he said.

Lincecum posted his first win of the season despite another uneven performance, Nate Schierholtz and Buster Posey homered and the San Francisco Giants beat the New York Mets 6-1 Monday in the first game of a doubleheader.

Slightly over 1,000 fans were in the stands when the opener began on a windy, raw afternoon better suited for the Bay Area and perhaps 10,000 were bundled up at the end. A rainout Sunday forced the twinbill.

Madison Bumgarner was set to pitch the second game for the Giants against Dillon Gee. San Francisco had won seven of 10 overall.

Battered in his first three starts, Lincecum (1-2) allowed one run in five innings and struck out eight, often throwing his fastball past the Mets. The two-time Cy Young winner also walked five and gave up four hits in lowering his ERA from 10.54 to 8.20.

Lincecum admits he'd been overthinking his recent outings.

"Your head's spinning and you're going to 50 different answers trying to get one," he said.

"We get caught up in negatives so easily," he said, "and forget about the positives."

Lincecum got help on his 108th and final pitch. With the bases loaded, one out and the Giants ahead by five runs, Ike Davis hit a grounder up the middle. Second baseman Emmanuel Burris stopped the ball and made a backhanded flip with his glove to shortstop Brandon Crawford, who barehanded the toss and turned a terrific double play.

Lincecum won his fourth straight start against the Mets, never permitting more than one run in any of them. Shaky in the first inning this year, he struck out three of the first five batters.

"I can't always expect big results," he said.

Miguel Batista (0-1) lasted only 3 2/3 innings in a spot start. The 41-year-old righty began the game by pitching out of the stretch -- fittingly, the Giants had runners on base against him all day.

"I missed my location I would say three times, cost me two runs," Batista said. "Posey hit a good pitch, I was surprised. The other guy, it was right down the middle."

Pablo Sandoval hit an RBI single in the first, but was thrown out trying to stretch it into a double. Posey followed with his home run.

Schierholtz hit a three-run homer in the third, set up by first baseman Davis' two-out, none-on error. Schierholtz also tripled and singled and Crawford added an RBI double.

Mike Baxter doubled home the Mets' run in the second after a two-out walk.

The Mets lost for the fourth time in five games. A bright spot for them: Jeremy Hefner, promoted hours earlier from Triple-A Buffalo, pitched three scoreless innings in his major league debut.

Game notes

Posey is 2 for 2 for two homers against Batista. ... Sandoval has a 15-game hitting streak. The San Francisco record at the start of a season is 16 by Willie Mays in 1960, STATS LLC said. ... Marlins SS Jose Reyes makes his return to Citi Field on Tuesday night when Miami visits the Mets. "He was a dynamic, exciting player for us. I think he deserves a warm reception from our fans," Mets GM Sandy Alderson said. "I hope he gets a good reception." ... Johan Santana (0-2, 3.97 ERA), pushed back a day by the rainout, starts for the Mets on Tuesday against Marlins ace Josh Johnson (0-2, 5.94). ... Matt Cain (1-0, 1.88) starts for the Giants on Tuesday night at Cincinnati. ... Giants 2B Freddy Sanchez (dislocated right shoulder) begins a rehab assignment Monday night for Class A San Jose. Giants manager Bruce Bochy said the team had mapped out an 18-day rehab for Sanchez.