Appointed earlier Wednesday evening as a short-time left fielder, Ryan Zimmerman watched the ball slice off Brandon Crawford’s bat and sail into the left field corner at AT&T Park. Tanner Roark stood on the mound, hoping another stellar start would remain unblemished. Michael Morse danced off second base, where he had reached on account of Zimmerman’s arm. Zimmerman reacted immediately, sprinting to his right.

“Just go for the ball, I guess,” Zimmerman said. “I’m kind of learning on the fly.”

Other developments were more responsible for the Washington Nationals’ 6-2 victory over the San Francisco Giants, beginning with Giants starter Matt Cain walking the first three batters of the game. Other moments led to the Nationals’ 10th win in 12 games, including Jayson Werth’s first home run in nearly a month, his two-run single in the ninth and Roark’s six strong innings. But no play stirred more drama, or whipped the Nationals’ dugout into a wilder frenzy, than the play Zimmerman made to end the sixth inning.

“It’s remarkable, really, to see him change positions and look so natural,” Werth said. “It’s not beginner’s luck or anything. He’s getting good reads. He’s running good routes. I said the other day, he makes left field look small. As an outfielder, that’s the ultimate compliment.”

Zimmerman’s diving catch, his best moment yet in left field, helped the Nationals claim their four-game series against the Giants before Thursday’s finale. The Nationals also seized sole possession of first place in the National League East after the Atlanta Braves fell in Colorado. The Nationals arrived at AT&T Park to face the best team in the National League. If they can pull off a sweep Thursday — their record aside — they may leave for St. Louis with the title attached to them.