SAN FRANCISCO - The typical baseball evaluation of Jordan Zimmermann, in whatever unscientific terms these things are set, is that he's a No. 2 starter, a pitcher who's capable of being near the top but not at the front of a major league rotation. The Nationals' ideal future is almost always phrased with Stephen Strasburg at the top of the rotation and Zimmermann at his side, like some kind of trusty aide.

At the moment, though, Strasburg is limited to throwing fastballs at less than full speed in bullpen sessions in Florida. While he's recovering from Tommy John surgery, Zimmermann is leading the rotation, but not by default. He's grabbing the role, and what he did on Tuesday night was only the latest example of it.
He allowed a run on five hits in seven innings, throwing just 91 pitches and putting the Nationals in position to win with little offense, some of which had been created by Zimmermann himself. And when Washington held on for a 2-1 win, most of the credit belonged to the 25-year-old.
"For me, the definition of a No. 1 starter is stopping losing streaks and picking your team up," said bench coach John McLaren, who managed the team with Jim Riggleman serving a one-game suspension. "That's what he looked like - a No. 1 starter. A tough game last night, we bounced back tonight, and he pitched great."
At a minimum, the Nationals needed Zimmermann to go deep in the game, with their bullpen having worked 5 2/3 innings in a 13-inning loss to the Giants the night before. But Zimmermann gave them more than that, shutting the Giants down after a pair of extra-base hits in the second inning. He had two sacrifice bunts, driving in a run with his second one, and despite scratching Jayson Werth from a lineup already missing Ryan Zimmerman, the Nationals had enough offense to win.
He's now made seven consecutive quality starts; he'd only had back-to-back quality starts once in his career before this year. Zimmermann has also cut two things out of his game that had hurt him in the past. He'd given up home runs on only 3.4 percent of his fly balls before tonight, compared to 12.2 percent in 2009 and 22.2 percent in a month in the majors after Tommy John surgery last year. And he's been able to stop innings from getting out of control; on Tuesday night, he allowed a an Aubrey Huff triple and a Nate Schierholtz double to start the second, and gave up only three singles the rest of the way.
"Last year, and the year before that, I probably would have got a little rattled in that situation, made some more mistakes and left balls over the middle," Zimmermann said. "This year, I'm telling myself, 'Let that one run score, and don't let any more score after that.' In past years, I would have said, 'I've got to try to stop this run from scoring,' and I guess that's the difference."
Zimmermann is also locating his fastball effectively for the first time in his career; he had the seventh-most valuable fastball in the National League before tonight's game, and used it to set up two sharp breaking balls on Tuesday. Zimmermann entered the game having thrown first-pitch strikes on 65.2 percent of his pitches, more confident than he's been in the past in his infield's ability to turn ground balls into outs.
He's reluctant to think of himself as the ace of the staff, saying there's no one in the Nationals' rotation who wears that title more than anyone else. But Zimmermann leads the staff in ERA, WHIP, walks, homers and strikeouts. Whatever he'd like to call it, he's leading the staff. He did it again on Tuesday.
"I think he's starting to realize how good he is," shortstop Ian Desmond said. "He's not backing down from anybody."