Mets starting pitcher Zack Wheeler adjusts his cap during the...

Mets starting pitcher Zack Wheeler adjusts his cap during the first inning against the Nationals at Citi Field on Tuesday. Credit: Kathleen Malone-Van Dyke

Zack Wheeler is in a battle to keep a spot in the Mets rotation. Jason Vargas is nearing a return from surgery on his non-throwing wrist and the lefthander is making his rehab appearances on the same days that Wheeler is making big-league starts. Yet with the kind of grit the righthander showed Tuesday against the Nationals, it might not be an easy decision.

Wheeler did not have swing-and-miss stuff and put enough men on base to be worthy of inclusion in a traffic report. Still, he hung tough and kept the damage low to give the Mets a chance to win.

He gave up three runs in six innings, which is a respectable performance. That he did it while allowing 10 baserunners — seven on hits and three on walks — speaks to the intestinal fortitude he displayed. He left trailing by a run and ended up the loser in the 5-2 defeat.

“I’ve always prided myself on it: A guy gets to second and don’t let him get to third or score,” Wheeler said. “It might be obvious, but I really concentrate on that, shutting the guy down at second . . . and giving the team the best chance to win.”

Wheeler escaped a bases-loaded jam by inducing an inning-ending double play in the first and allowed three runs on a sacrifice fly and two soft singles. The Mets were down 3-0 and he helped make it a 3-2 game before he exited, starting a two-run rally in the fifth with his second single of the game and sliding home on Asdrubal Cabrera’s sacrifice fly.

In the Mets’ rotation, Wheeler’s already been outside-looking-in once. When the Mets broke camp, Wheeler went to Triple-A Las Vegas and Seth Lugo was tabbed to stand in as the fifth starter. Lugo’s first start became unnecessary because of a postponement and he became a big weapon from the bullpen. When another starter was needed last week, Wheeler delivered seven innings of one-run ball to beat Miami.

Manager Mickey Callaway said no plan is set in stone and plenty could happen before Vargas returns, in at least 10 days.

“You’re trying to prove that you belong here . . . but at the same time you have to go out and pitch,” Wheeler said. “I think I belong here and sometimes it’s just a numbers game. I don’t let that bother me and I actually try to use that as motivation to go prove my case.”

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