The Nationals are now 17-16 since Ryan Zimmerman last played, an expectation-surpassing record built on many factors. Their rotation has punched up a 3.83 ERA while throwing 6 1/3 innings per start. Their defense has made 17 errors, including just two in the last 17 games. Drew Storen is 3-0 with nine saves and a 0.00 ERA in 18 innings.

But, you know, someone has to play third base, too.

Most often, 21 times in 33 games, that someone has been Jerry Hairston. When the Nationals signed Hairston this winter, they wanted an option in center field against left-handed starters and a middle infielder to help shepherd Ian Desmond and Danny Espinosa. He could play third base, but why would the Nationals ever need that?

“That’s really my job,” Hairston said last night. “I know I’m not Zim. Zim’s our best player. I try to do what I can do. I try to do my job, and just be solid over there and get some hits every once in a while.”

Hairston has actually been coming on lately, going 12 for his last 36 with five extra-base hits, including a home run Monday night. In the fifth inning, with two outs and the score tied at 1, Hairston worked a 2-0 count against Paul Maholm. He sat fastball, and when Maholm unfurled a changeup, Hairston took a vicious hack that produced only a stiff breeze.

“I kind of sold out a little bit,” Hairston said. “He kind of embarrassed me. I had a little smile. I said, ‘That’s what I get.’ ”

After another ball made the count 3-1, “I still wanted to be aggressive,” Hairston said. Maholm threw an 88-mph inside, belt-high fastball. As soon he finished swinging, Hairston knew. He skipped out of the batter’s box and watched the ball soar over the fence, into the Pirates bullpen.

It was Hairston’s second homer this year. Surely, Zimmerman would have more right now. But Hairston knows he is not Zimmerman. He’s doing what he can do, and for the Nationals, that’s been just enough.