Jeremy Hefner certainly enjoyed his whirlwind visit to the big city.

Major league debut, three scoreless innings.

That was about all that went right for the New York Mets. Behind Madison Bumgarner, Tim Lincecum and several home runs, the San Francisco Giants swept a doubleheader, finishing it off with a 7-2 win Monday night.

Summoned from Triple-A shortly before noon, Hefner arrived at Citi Field soon before gametime.

"This is my first time in New York City, first time seeing the Statue of Liberty, so it was really cool," the Oklahoma-born Hefner said.

Hefner came in to begin the fifth inning and the first hitter he faced was Buster Posey. The right-hander retired the Giants star on a grounder, and wound up allowing three hits and a walk.

After the 6-1 loss, the Mets sent the 26-year-old Hefner back to Buffalo and promoted infielder Jordany Valdespin from the minors.

"You're on a high whenever you get over here. Getting sent down, it's kind of a bummer. But I'll enjoy it while I'm here," Hefner said.

"I had a good outing, so everything went well," he said. "Hopefully, I contributed, and I'll go back down and keep working on my craft. When they need me, I'll be back."

Hefner had been scheduled to start at Lehigh Valley on Monday night when he was called up. He took a car service for the 2-hour ride, arriving in time for the doubleheader that was set to begin at 4:10 p.m.

"I was more nervous on the drive over," he said. "When I got here, I was fine."

Mets starters Miguel Batista and Dillon Gee did not fare as well. New York lost for the fifth time in six games and dropped to .500 for the first time this year.

"They're a tough team to pitch against. They run all those switch-hitters at you. They just outhit us and outpitched us tonight. It was pretty simple," Mets manager Terry Collins said.

Batista (0-1) lasted only 3 2-3 innings in a spot start in the opener. 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.

Posey and Nate Schierholtz homered to make it 5-1 after three innings.

"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."

Gee (1-2) gave up seven runs and a career-high 12 hits in 6 2-3 innings.

"That's one to forget right there," Gee said. "There's not a whole lot I can say about tonight. Obviously, I just came out in the first inning and set a really bad tone in the game for us and continued to live up in the zone all night long, and they hurt me."

Both games were similar: Pablo Sandoval put San Francisco ahead for good in the first inning, the Giants supported their starter with two home runs, and they got plenty of pitching.

The Mets got a bit banged up, too. Left fielder Jason Bay bruised his ribs trying to catch Gregor Blanco's two-run double in the second game. The ball bounced out of Bay's glove and he landed face-first on the grass near the warning track. X-rays were negative and Bay will be re-examined Tuesday.

Slightly more than 1,000 fans were bundled up in the stands when the opener began on a windy, raw afternoon better suited for the Bay Area, and the ballpark was mostly empty at the end. A rainout Sunday forced the twinbill.

The Giants took the opener as Lincecum (1-2) posted his first win of the season despite another uneven performance.

Bumgarner pitched seven neat innings and Sandoval homered to match a team mark set by Willie Mays in the nightcap.

Bumgarner (3-1) allowed one run and three hits. He won his third straight start, a streak that began shortly before the 22-year-old lefty signed a $35.56 million, six-year contract.

Sandoval hit a three-run homer in the first inning to back Bumgarner. The burly slugger has a 16-game hitting streak, tying the San Francisco record at the start of a season set by Mays in 1960, STATS LLC said.

"Willie Mays is one of the greatest," Sandoval said. "Everything's going well."

Hector Sanchez later hit his first big league homer, a two-run shot.

NOTES: 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).