SAN DIEGO (AP) -- The San Diego Padres are having a mercurial season.
Swept by the Giants in San Francisco last weekend, the Padres returned the favor by taking three games from the defending World Series champions at Petco Park.
Chase Headley, Nick Hundley and Alexi Amarista homered off Ryan Vogelsong to lead the Padres to a 6-4 victory Sunday. It was San Diego's first three-game sweep of the Giants since May 2010.
It was the fifth sweep the Padres have been involved in this season. After losing three games at home to Colorado two weekends ago, the Padres turned around and beat the Dodgers in three straight at Los Angeles.
''Can't explain it. Wish I could,'' manager Bud Black said. ''Baseball's a game a lot of times that's unpredictable. You never know how a month's going to play out, or let alone a week. It's good to see we were able to come out today and get Vogelsong and Jason (Marquis) did his thing. Wish I could explain it.''
The Padres remain in last place in the NL West but feel they're playing better. They hit better in this series than they did in San Francisco and got some nice defense.
''We're definitely playing a lot better baseball right now,'' said right fielder Chris Denorfia, who saved two runs with an impressive diving catch of Andres Torres' fly ball with runners on second and third and two outs in the eighth. ''Our pitching's been outstanding the last week, maybe more. Our hitting's coming around. We've got Chase and Carlos (Quentin) back in the lineup so we're starting to be the team we knew we could be coming out of spring training.''
Headley had three hits and Amarista scored three runs for the Padres, who've won four straight.
''It's great to see some guys hit some home runs today,'' Headley said.
The difference between the two series with the Giants was ''not all that much, to be honest,'' Headley said. ''We executed the little things, we're making plays defensively and got a couple of big hits. Our pitching did a nice job for us. Not a huge difference but enough to swing the series.''
Pablo Sandoval had an RBI single among his career high-tying four hits for the Giants, who lost their season-high fifth straight game. They've lost eight of 12 following a 9-4 start.
''We haven't been playing so well,'' manager Bruce Bochy said. ''We've been making mistakes that have hurt us in this little streak we are in. Guys could use a little break, too. It's a tough series. You're going to have them, as much as you don't like them. We're going to deal with it.''
Buster Posey extended his hitting streak to nine games with a two-run homer to pull the Giants to 6-4 in the eighth. Sandoval was aboard after his third single.
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 bottom of the inning 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.
''It's a battle from the start for Vogy,'' Bochy said. ''He didn't have good stuff or command. It was just a case where he was battling without his good stuff. He made some mistakes. The ball was up quite a bit and they didn't miss 'em. This usually is a ballpark that is a little bit forgiving. But the ball was carrying pretty good today. He got the ball up and they took advantage of it.''
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).