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SAN FRANCISCO -- Pablo Sandoval says he had never hit a game-ending homer at any point in his baseball journey from northern Venezuela to San Francisco.

If he had ever tripped on the dirt and faceplanted while trying to stretch a double into a triple, he wasn't about to admit that, either.

This promising season is just full of new experiences for the 22-year-old slugger and his jubilant Giants teammates.

Sandoval's three-run homer with two outs in the ninth ended San Francisco's wild 9-7 victory over the Washington Nationals on Tuesday night.

"I couldn't believe that happened for me," said Sandoval, a free swinger who uncharacteristically took four pitches before his homer. "In this moment, I'm just going to get my pitch and drive the ball. I don't want to tie the game. I just want to end it."

Ryan Zimmerman extended his hitting streak to 30 games with two singles for the hard-luck Nationals, who have lost nine straight to the Giants -- none tougher than this defeat after Washington scored six runs in the late innings. San Francisco blew a 5-1 lead when Nick Johnson hit a three-run homer in the seventh and drove in two more runs with a weak single in the eighth.

But after Bengie Molina hit an eighth-inning homer off Kip Wells, the Giants rallied in the ninth against Joe Beimel (0-2), Washington's setup man getting a chance to close.

Emmanuel Burriss singled and Edgar Renteria drew a walk before Sandoval cracked a 2-2 pitch into left for his third homer of the season, setting off a frenzied celebration at home plate for the Giants' 15th win in 21 games, pushing them four games above .500 for the first time in nearly three years.

"When he hit it, I was like, 'No way,'" Burriss said. "When I saw that ball go out, I just felt like a little kid. My celebration was probably bigger than his."

Sandoval thoroughly atoned for his baserunning blunder two innings earlier, when he tripped and landed face first while trying to stretch an extra-base hit. He stayed down for several moments out of embarrassment, not injury.

"Kung Fu Panda doesn't get hurt," Giants starter Matt Cain said, citing Sandoval's cinematic nickname.

Brandon Medders (2-1) got two outs in the ninth for San Francisco, while Washington's disastrous bullpen flopped again.

"We've tried everybody and their cousins, and we still can't get anybody to put up a zero up there in the eighth and ninth inning," Washington manager Manny Acta said. "That's really just killing us. That's very discouraging, to waste the type of offense that we're displaying out there for a month and a half now, and we still don't have much to show for it."

Zimmerman went 2-for-5, getting both hits off Cain while matching the fourth-longest hitting streak in the majors since 2000. He has the first 30-game streak since Moises Alou did it in late 2007, and the 26th streak of at least 30 games since Joe DiMaggio's 56-game record in 1941.

Washington's third baseman also is one game shy of the franchise-record 31-game streak by Montreal's Vladimir Guerrero in 1999.

"Our starting pitchers are the youngest part of our team, and they've done well," Zimmerman said. "Unfortunately, the guys that are pitching the second half of the game haven't been able to get it done this year, and that's been the story of our season so far."

Rookie starter Jordan Zimmermann allowed six hits and struck out eight during six innings for the Nationals.

Randy Winn and Renteria drove in two runs apiece for the Giants, while Cain yielded nine hits and four runs. Cain gave up Johnson's homer in the seventh, and struggling reliever Bob Howry gave up pinch-hitter Ronnie Belliard's two-out RBI single in the eighth to tie it.

Game notes

Molina drew his first walk of the season in the first inning. San Francisco's free-swinging cleanup hitter then struck out twice before his homer. ... CF Elijah Dukes was scratched from the starting lineup with an apparent illness, but he entered the game in the ninth.