The San Francisco Giants won last year's World Series behind excellent starting pitching and a stingy bullpen.

Lately, most everyone who takes the mound for them has struggled.

Jordan Zimmermann hasn't had any issues recently - or many at all against San Francisco - and he'll look to lead the Washington Nationals to a ninth straight home win and three-game sweep of the slumping Giants on Sunday night.

San Francisco (42-20) has a 6.08 ERA during a five-game losing streak after World Series MVP Madison Bumgarner gave up three runs on the first five pitches and six over five innings of Saturday's 9-3 defeat.

Michael Taylor homered on the first pitch, Yunel Escobar hit a home run on the second and Bryce Harper followed with his 25th homer to help deal the Giants a sixth consecutive road loss, a stretch in which they've been outscored 37-18.

San Francisco's overall losing streak began Tuesday, when Ryan Vogelsong allowed four runs in six innings of a 5-3 defeat at Miami after pitching 12 2-3 scoreless to win his previous two outings.

Vogelsong (6-6, 4.19 ERA) gave up two homers, matching the amount he surrendered over his previous 10 starts.

''It's tough to take,'' Vogelsong said. ''How many pitches did I throw? And you think about two. I just left the ball up a little bit.''

The right-hander has allowed one home run in six career starts against the Nationals, but he's gone 1-2 with a 6.67 ERA in those outings. That stretch, however, includes Game 4 of the 2014 NLDS in which he allowed one run and two hits in 5 2-3 innings of San Francisco's series-clinching 3-2 victory.

Zimmermann (6-5, 3.16) tossed a gem in Game 2 of that series, holding the Giants scoreless for 8 2-3 innings before exiting after walking Joe Panik. He was charged with a run after Panik came around to score to tie the game, which San Francisco won 2-1 in 18 innings.

Despite not earning the victory, the outing gave Zimmermann a 1.99 ERA in his last eight starts against the Giants. The right-hander has put up even better numbers over his last two outings, allowing six hits in eight scoreless innings of a 2-1, 11-inning win over Atlanta on June 24 and pitching 7 2-3 scoreless in Tuesday's 6-1 victory over the Braves.

"His past couple of starts his breaking ball has been really, really good," first baseman Clint Robinson sad. "He's been able to get that in there first pitch, get ahead of the hitters and then put hitters away."

Washington won Friday's series opener by a 2-1 score after Robinson hit a go-ahead two-run homer in the seventh. Robinson had another solid day Saturday, going 2 for 3 and scoring twice.

Harper has homered in five of his last seven against the Giants, including playoffs, and finished a triple short of the cycle Saturday for the Nationals (45-36), winners of 11 of 14.

Giants outfielder Angel Pagan didn't start for the second straight contest because of a swollen left knee. His status for Sunday is uncertain.

SI Apps
We've Got Apps Too
Get expert analysis, unrivaled access, and the award-winning storytelling only SI can provide - from Peter King, Tom Verducci, Lee Jenkins, Seth Davis, and more - delivered straight to you, along with up-to-the-minute news and live scores.