SAN FRANCISCO -- It was bad enough a reeling Washington Nationals team had to face San Francisco Giants ace Madison Bumgarner Sunday afternoon.

To have to deal with him at the plate as well proved to be overkill.

Bumgarner contributed a double and a home run to his 14th victory of the season, hitting and pitching the Giants to a 5-0 win over the Nationals that completed a four-game sweep.

"He did it all," Giants manager Bruce Bochy gushed. "That's an impressive outing with how hot it was. That game is right up there with the best he's thrown, (and) he's thrown a lot of them."

In completing a 5-1 homestand, the Giants wrapped up a 4-3 season-series victory over the Nationals despite having gotten swept in a three-game series in Washington in July.

The loss dropped the Nationals (58-59) under .500 for the first time since May 6. They have opened a 10-game trip with six losses in seven games.

"We have to play better," assured Nationals first baseman Ryan Zimmerman. "We've played terrible the last 15 or 16 games and we faced one of the best today. He might be the best in the bigs right now."

Washington has lost 20 of its last 29 games.

Bumgarner dominated the Nationals on the mound, shutting them out on three hits -- a fifth-inning single by shortstop Ian Desmond, a broken-bat single by catcher Wilson Ramos in the eighth and a one-out single by second baseman Anthony Rendon in the ninth.

It was the fourth shutout of the 2014 World Series Most Valuable Player's career.

In winning for the sixth time in his last seven decisions, Bumgarner (14-6) walked one and struck out a career-best-tying struck out 14, the fifth double-digit effort of the season and 24th of his career.

"You can always do better," Bumgarner said after matching a 14-strikeout game against the San Diego Padres on June 23, "but this would be tough to beat."

The complete game was his second in a row, third this season and ninth of his career.

It came on a day when the Giants were honoring one of their all-time greats, Hall-of-Famer Juan Marichal.

"That was an old-school type game," Bochy related. "The starter goes nine ... (That) was fitting. Marichal did it so many times."

The Giants got all the runs they would need in a three-run uprising against Nationals starter Joe Ross in the fourth inning. Then Bumgarner basically single-handedly did the rest offensively himself.

His hit-and-run RBI double in the fifth inning scored second baseman Kelby Tomlinson, who had singled, to increase the Giants' lead to 4-0.

Bumgarner then capped the scoring in the seventh with a solo homer against Nationals reliever Casey Janssen. It was the 2014 Silver Slugger Award winner's fourth homer of the season and 10th of his career.

Clearly, the right-handed hitter was more impressed with his double to the opposite field.

"Obviously I don't do that very often," he said. "It sure worked out for us."

Right fielder Hunter Pence also had a homer, a two-run shot that was his ninth of the season, as part of the Giants' fourth-inning uprising.

First baseman Brandon Belt doubled in center fielder Gregor Blanco, who had walked, to open the scoring earlier in the inning.

Blanco finished the game with a hit and two walks in his four plate appearances.

"It's not easy to record a four-game sweep," Bochy noted. "We certainly had to play our best ball, and we did it. These guys just elevated their game when we needed it."

The Nationals' Ross (3-5) failed to get out of the fifth inning. He allowed six hits, four of which went for extra bases, and four runs in four-plus innings. He walked one and struck out six.

"There's a little more pressure (when you're pitching against Bumgarner). You think about it going into the game," Ross said. "But you still have to go out there and pitch. I made a few mistakes and thing added up on me."

The Giants out-hit the Nationals 7-3.

NOTES: The shutout was the Giants' 15th of the season, which ranks second in the National League. ... Giants RHP Madison Bumgarner leads all pitchers with four home runs this season. ... The first-pitch temperature of 85 degrees at AT&T Park was one degree off the all-time stadium record set in 2010. ... Nationals CF Denard Span (sore lower back) was scheduled to begin an injury-rehab stint at Class A Potomac on Sunday night. Span hasn't played since July 9. The Nationals are 35-24 with Span in the lineup and 23-35 without. ... After taking Monday off, the Nationals complete a 10-game trip with a three-game series at Colorado beginning Tuesday. ... Giants CF Angel Pagan (patella tendinitis in right knee) and 2B Joe Panik (inflammation in lower back) will go to Arizona for physical therapy while the club visits St. Louis and Pittsburgh this week.