Nationals third baseman Ryan Zimmerman watches his RBI double in an 8-6 vicory over the Cardinals this month. (ANN HEISENFELT/ASSOCIATED PRESS)

Let’s pretend you are an unmarried ballplayer in your mid-20s, in the third year of a $45 million contract with a major league club. And, as part of that deal, your agent negotiated a clause in which you had full use of your home ballpark for one night a year.

No men on base. No pressure to drive home a run. No consequences if you swing and miss. For one night, no umpires — you make the rules.

You’re single, rich and famous.

What would you do? Whom would you invite?

Would there be wine, women and song or a keg, friends and paintball?

“We’ve had some interesting conversations with my buddies about what I should do at the park for one night, kind of to that effect,” Ryan Zimmerman said, chuckling, a few days before the Washington Nationals unlock the gates Thursday for Night at the Park II.

There is no bacchanalia, no police raid — no turning the top of the dugout into a party deck. But there is Rodney Atkins’s crooning, David Blaine’s magic and the host who plays third base for the home team, who has a social conscience belying his 26 years.

“It just felt right,” said Zimmerman, who directs all proceeds from the event to his ziMS Foundation, which fights multiple sclerosis, a disease his mother Cheryl had diagnosed in 1995. “It just felt like kind of my duty to give back.”

With Blaine making his second appearance, it has to be asked: Other than the night Zimmerman launched a two-out, walk-off home run in the bottom of the ninth inning to open Nationals Park in 2008, or the time he tossed his batting helmet into the air with glee as his dad, Keith, smiled from the stands on Father’s Day in 2006, or the 30-game hit streak in 2009, can the great magician make much of the last six years disappear?

“I don’t know if he can pull off that miracle,” Zimmerman said, wryly. He paused for a second. “For us, we’ve kind of forgotten about those times.”

It would be a tragedy if Zimmerman never played for a contending team during his time here, if Washington’s first draft pick, who holds 21 of 22 Nationals batting records, never had the pieces around him to play in October.

“I think it’s been kind of a long road, especially for me,” Zimmerman said. “I’ve been here for four or five years now and it’s been some tough years. To finally see some of the young guys grow up and kind of mature a little bit. We still have a ways to go, and it’s just the tip of the iceberg now. But to play quality baseball and be on a quality team that the fans want to come watch every night is gratifying.”

How many times can Zimmerman be trotted out at a news conference announcing another bonus baby, only to sift through another frustrating season of injury and losses and wonder when things will turn for good? He holds up a Stephen Strasburg jersey or a Bryce Harper jersey, the kids shake his hand and he welcomes them to the big leagues and hopes beyond hope their bodies and minds are healthy enough to help within a year.

“I’ve been very patient,” he said. “But that’s okay.”

Stable, humble, always taking the high road, Zimmerman has comported himself better than any leader of any Washington team.

Zimmerman was 11 when his mother, a tremendous lacrosse player in college, had MS diganosed and he was 16 when the disease confined her to a wheelchair. His entire adolescence was spent worrying about someone else.

“It made me and my little brother kind of learn to do things a little bit more,” he said. “But one thing, she never let it affect how me and my brother grew up. The most impressive thing about it is, still to this day, she won’t let it keep her down.”

Said Keith, his father, by telephone Wednesday afternoon: “Lots of parents pull their hair out when their kids reach a certain age, but Ryan and his younger brother never gave us any of that kind of trouble. They were just even-keel, good kids. I’m proud of ’em.”

Keith and Cheryl will be in attendance Thursday night for the festivities, the one night a year a rich, young and famous baseball player exercises the right to use the field for whatever he chooses before he goes back to work and waits for reinforcements in 2012.

“That’s the tough thing with baseball,” Zimmerman said. “In order to be good for a long time, you got to start from the bottom up. Now we’re starting to see the rewards and benefits for being so patient. That’s the scary thing. We’re only seeing a couple of young guys now. There’s still three or four guys in the minor leagues. It’s pretty impressive what we’ve got coming.”

It’s also pretty impressive what the Nationals have had here since 2005.

What I wish for Ryan Zimmerman? I wish him a night at the park in October.

House full. Bases full. Count full. And a ball disappearing deep into the night, followed by the bedlam brought on by winning a series with one wicked swing.

It’s the least he deserves for shepherding a franchise through the past six seasons, still the selfless adult who had to grow up early, looking out for others before himself since he was 11.