SAN DIEGO — The San Francisco Giants played some regulars Sunday who might have otherwise rested after a night game and it still didn't keep their losing streak from reaching a season-high five games.
Chase Headley, Nick Hundley and Alexi Amarista homered off Ryan Vogelsong and the San Diego Padres beat San Francisco 6-4 Sunday for their first three-game sweep of the Giants since May 2010.
Headley had three hits and Amarista scored three runs for the Padres, who've won four straight.
"It's always frustrating when you lose but I don't sense any tension or anybody overly frustrated," said Buster Posey, who hit a two-run homer in the eighth to pull the Giants within two runs. "It's more of a drive and willingness to want to work to get back on track."
Pablo Sandoval had an RBI single among his career high-tying four hits for the defending World Series champion Giants, who've lost eight of 12 following a 9-4 start. The Giants swept the Padres the previous weekend in San Francisco.
Posey extended his hitting streak to nine games with his homer, which came with Sandoval aboard after his third single. With runners on second and third and two outs, San Diego right fielder Chris Denorfia made a nice diving catch of Andres Torres' fly ball.
"You look at the last five games and they very easily could have gone our way," Posey said. "We're playing some tight games, so we have to keep on grinding and we will be all right. We have guys on this club who have been around for a while and understand the ups and downs of the season. I'm not too concerned."
San Diego's Jason Marquis (2-2) bounced back from a 7-1 loss to Milwaukee on Monday night in which he allowed a season-high seven runs, including first-inning homers to Ryan Braun and Yuniesky Betancourt.
Marquis pitched out of trouble after loading the bases in both the second and third innings. He allowed two runs and six hits in 6 2-3 innings, walked four and struck out three.
Headley and Hundley each hit their second homer of the year while Amarista had his first. The Padres are the only team in the majors that doesn't have a player with at least three homers.
Headley homered to straightaway center field with two outs in the first.
After Brandon Crawford hit a sacrifice fly to tie it in the second, Hundley hit a two-run shot into the balcony on the second level of the Western Metal Supply Co. brick warehouse in the left-field corner with two outs in the second to give San Diego a 3-1 lead. Amarista was aboard on a single.
With rookie Jedd Gyorko aboard on a leadoff double, Amarista hit a two-run homer in the fourth that landed on top of the new right field fence and bounced over the Jack Daniel's Old No. 7 Deck and into the seats. It was the first time the Padres benefited from the new fence, which was moved in 11 feet in an attempt to make the spacious downtown ballyard play fairer.
Opponents have hit four homers that wouldn't have gone out last year, including Posey's shot in the eighth that ticked off the glove of leaping right fielder Chris Denorfia. It was Posey's third.
Amarista walked leading off the sixth. Hundley singled to chase Vogelsong and the runners advanced on Marquis' sac bunt. Amarista scored on Posey's passed ball to make it 6-2.
The Giants loaded the bases with one out in the second before Brandon Crawford hit a sacrifice fly. Marquis struck out Vogelsong to get out of the jam.
San Francisco loaded the bases again with one out in the third before Marquis got Hunter Pence to hit into a double play.
Vogelsong (1-2) went five-plus, allowing six runs, five earned, and eight hits, struck out six and walked three.
Huston Street pitched the ninth for his fifth save in five chances.
NOTES: San Diego swept the Giants for the first time since May 11-13, 2010, at San Francisco. Their last home sweep of the Giants was April 19-21, 2010. The Padres led the NL West for much of that season before staggering down the stretch and being eliminated from playoff contention on the last day by the Giants, who went on to win the World Series. ... Posey has nine RBIs and six extra-base hits during his hitting streak. ... The Padres travel to Chicago to open a four-game series against the Cubs on Monday. LHP Clayton Richard (0-2, 7.94) is scheduled to start against Jeff Samardzija (1-4, 3.03). ... The Giants open a series at Arizona on Monday night, with RHP Matt Cain (0-2, 6.59) scheduled to start against Ian Kennedy (1-2, 4.70).