WASHINGTON -- On a day when the Washington Nationals weren't hitting, Wilson Ramos supplied all the offense that was needed.

Ramos hit a tie-breaking homer in the seventh inning, Tanner Roark pitched seven strong innings and the Nationals defeated the San Francisco Giants 1-0 on Sunday, taking the deciding game in a series pairing the National League East and West Division leaders.

Leading off the seventh against Madison Bumgarner, Ramos lifted an 0-1 slider to the opposite field for this 18th homer of the season, and just the Nationals' second hit of the day.

"When he hit it, it looked like he put his head down like he was disappointed," Bumgarner said. "So I turned around and was waiting on (right fielder Gregor) Blanco to catch it, but it just kept going."

Ramos is second in the league with a .338 average and leads all catchers in home runs. He's hit safely in 19 of his last 23 games.

"His confidence level is high, really high," manager Dusty Baker said of his All-Star catcher.

"He can reach the fences in any part of the ballpark, but remains within himself. He doesn't try to hit home runs all the time."

Roark (12-6) allowed five hits and pitched out of trouble all afternoon while striking out five and walking three. It was his league-best seventh start in which he has allowed no runs over seven or more innings.

"This guy, he continues to ... he's not amazing us anymore, we've kind of come to expect it," Baker said.

Just prior to the Ramos homer, Washington center fielder Ben Revere used his speed and glove to preserve the tie.

After first baseman Daniel Murphy's error left runners on second and third with two outs in the seventh, Revere made a running over-the-shoulder catch on the warning track to rob Brandon Belt.

"I knew he got good wood on it, but I didn't even see it," Roark said. "Then I saw Ben just racing back and I was like 'Oh man, come on.' Then he made that over-the-shoulder catch. It was a heck of a play. Unbelievable."

Mark Melancon worked a 1-2-3 ninth for his 31st save and first as a member of the Nationals.

The Giants (63-48), who have lost four of six on their road trip, went 1-for-9 with runners in scoring position.

Bumgarner (10-7), coming off his worst outing of the season, was back in form. Aside from the home run, he allowed only Anthony Rendon's fourth-inning double and a pair of walks to go along with seven strikeouts and a hit batter over eight innings.

"I knew he'd pitch well today, that's just who he is," manager Bruce Bochy said of Bumgarner, who allowed eight runs -- four earned -- in his last start. "There was no question that he was going to bounce back."

Bumgarner is still looking for his first win since the All-Star Break.

The Nationals (66-45) were without Bryce Harper, who has been bothered by a stiff neck.

San Francisco had several early opportunities against Roark, but stranded seven base runners from innings two through five.

The Giants had runners on first and second with no outs in the third, but Roark sandwiched strikeouts of Denard Span and Belt around a fielder's choice by Angel Pagan to keep the game scoreless.

In the fourth, San Francisco wasted a leadoff double by Buster Posey.

Joe Panik singled to center with two outs, but third-base coach Roberto Kelly held Posey at third as Revere's throw home sailed about 10 feet up the first base line. Blanco then grounded out.

"What I saw was [Revere] get to the ball pretty quick," Kelly said. "If I had it to do again, I probably send him with two outs."

Washington's Jayson Werth extended his consecutive games on-base streak to 38 with a walk.

NOTES: The Nationals won the season series 4-3. ... Giants RF Hunter Pence was not in the starting lineup on Saturday after staying in Friday's game following a scary situation. Pence fouled a ball that bounced in the dirt and struck him in the face in the second inning. He did pinch hit in the ninth on Sunday and struck out. ... Washington 2B Trea Turner came in hitting .353 (18-for-51) over his past 12 games. ... San Francisco pitchers began the day having allowed a league-high 32 homers since the start of the second half. ... Giants LHP Josh Osich (left forearm strain) began a rehab assignment with Double-A Richmond. ... San Francisco begins a three-game series on Monday at Miami, while Washington hosts Cleveland for two games beginning on Tuesday.