Nationals starter Jordan Zimmermann was not up to his usual high standards in San Francisco, yielding eight hits and two walks in 5 2/3 innings. The Nats and Giants will play a day game starting at 3:45 on Wednesday. (Robert Galbraith/Reuters)

The Washington Nationals’ supremacy has not made them immune from a worthy opponent. Tuesday night, they sent the National League’s ERA leader to the mound and bulwarked him with baseball’s best offense over the season’s second half. But an oppressive starting pitcher can still strangle the life out of their offense, same as any other team, no matter how invulnerable they appear.

The Nationals ran into the one thing that can stop any scalding contender cold. In their 6-1 loss to the San Francisco Giants, elastic-armed lefty Madison Bumgarner delivered a dominating pitching performance, allowing one run in a complete game a day after the Nationals dismantled the Giants’ pitching staff with 14 runs and a new park record for hits.

“That’s just the way this game works sometimes,” Nationals rookie outfielder Tyler Moore said. “It’s crazy. We scored 14 last night, and tonight they shut us down. We’ll come back tomorrow with a positive attitude and try to win a series.”

The Nationals’ bullpen imploded in a four-run eighth to seal the result. For most of the night, Bumgarner outdueled Jordan Zimmermann, who pitched around trouble but lasted 5 2/3 innings and allowed two runs while throwing 94 pitches.

The Nationals had won 11 of 13, and now they will have to win Wednesday to claim the series from the Giants, a team they had previously pulverized in all four meetings this season. Because the Atlanta Braves won before the first pitch at chilly AT&T Park, the Nationals’ lead in the NL East decreased to 4 ½ games.

Right fielder Jayson Werth returned to the Nationals’ lineup on the same day he received an MRI exam on the sore right ankle that forced him out of the lineup Tuesday night. Werth did not ease back into the action. He went 1 for 3 with a triple and fielded about a dozen balls in right field, and, afterward his ankle held up fine.

“It was good,” Werth said. “It was good. Like I told you last night, I kind of expected that was going to be the way it was going to go: a little tender, a little sore, but playable. I think it should be fine. It was pretty standard.”

Michael Morse, whose swollen thumb held him out Tuesday, vowed afterward that he’ll be coming back to face Tim Lincecum in the series finale. “I’m playing tomorrow,” he said.

Zimmermann was not himself, but still quite good. Bumgarner, a sidewinder who spreads his arms like pterodactyl during his windup, was exquisite. He fired darting cutters to right-handers, fooled lefties with wipeout sliders and spotted fastballs on the plate’s edges. Bumgarner allowed the Nationals five hits, walking one while striking out six. The Nationals did not push a runner past second base until the seventh inning, and the rallies they mounted withered on the stalk.

Manager Davey Johnson saw the Nationals’ best chance to beat Bumgarner was getting him out of the game. He sensed Giants Manager Bruce Bochy would have gone to his closer, Sergio Romo, in the ninth inning if they held the deficit at 2-1 in the eighth inning.

“I really felt we were going to win that ballgame if we just held them in the eighth,” Johnson said. “I thought we’d have a better chance.”

Johnson turned to Drew Storen, and any chance for a comeback evaporated. Storen faced five batters and allowed three hits and a walk. All four runners scored, two of them coming around after he handed the ball off to Sean Burnett. Since he returned from elbow surgery, Storen has vacillated between dominance and disaster. The inconsistency is natural for a pitcher in the early stages of coming back.

“It’s part of it,” Storen said. “I just got to make the adjustments. Missing down in the zone, that’s not normal for me. I just got to adjust my sights and go from there.”

Zimmermann kept his ERA at 2.38, still tops in the league, but the Giants smacked line drives and worked counts against him as few opponents have. Zimmermann allowed eights hits and walked two, constantly pitching his way out of a jam. Most innings, he limited damage, but not enough to beat Bumgarner.

“I didn’t have my best stuff, that’s for sure,” Zimmermann said. “I didn’t make the quality pitch when I needed to. . . . I was missing a little bit here and there.”

The Nationals entered the seventh trailing, 2-0, at which point close followers surely began to wonder how they would choose to win this particular game. Jayson Werth blasted a deep drive to right-center field off Bumgarner. The wind, a force field all night, held the ball up a bit, but Hunter Pence could not make the play. As Pence batted the ball around, Werth sprinted around the bases on his sore ankle and glided into third with a leadoff triple.

Adam LaRoche smoked a one-hopper at shortstop Brandon Crawford. The ball ate him up and trickled into shallow left field. Werth trotted home, making it 2-1, and the Nationals had finally mounted a substantive charge. Their recent play suggested a complete comeback in the offing. This time, Bumgarner snuffed it out. After two harmless flies to right field, Steve Lombardozzi struck out swinging through a chest-high fastball.

LaRoche’s single could have tied it if not for Zimmermann’s most crucial mistake. The 1-0 game churned into the bottom of the sixth, at which point the Nationals had mustered only three hits off Bumgarner, two singles by Danny Espinosa and another from Zimmermann. With one out, Zimmermann walked Pablo Sandoval on four pitches, no small feat against one of the league’s freest swingers.

Pence followed with a single, and Brandon Belt connected with another crucial blow. He obliterated a first-pitch, 92-mph fastball off the top of the towering brick wall in right field. Sandoval scored.

“I was just trying to go in and jam him,” Zimmermann said. “I just left it right over the middle. Anyone could have hit that pitch.”

After Belt jogged out of the box, admiring what he thought was a homer, Werth fired a throw to second base to retire him on the bases. Zimmermann would not get the chance to record the final out of the inning. As he handed the ball to Johnson, Zimmermann smoldered.

“I never wanted to get taken out in the middle of an inning,” Zimmermann said. “I was more frustrated there with the pitch I left right over the middle.”

The Nationals would report back to AT&T Park about 12 hours for the final pitch for a 12:45 p.m. start on the West Coast, ideal happy-hour viewing back home. The Nationals have one game left on a dominating road trip they have started 7-2. They will have a chance to finish it off right, so long as they do not run into another performance like Bumgarner’s.

“You’re not going to win every game,” Werth said. “You can only expect to put it all on the line, and we do that every night. We got to win the series and finish up a strong road trip. That’s all you can ask for.”