“A throw that short shouldn’t be as painful as it is,” LaRoche said. “If I could calm it down a little bit, that would be great.”

LaRoche has not thrown at full strength all year, ever since he showed up the first day of spring training with the first sore arm of his career. LaRoche received a cortisone shot at the end of the spring training, but after the two throws that hurt his shoulder this week, he feels his shoulder has regressed to where it was at the beginning of the spring. The recurring pain made LaRoche accept that the fraying in his labrum will be issue all year.

“It hurts to throw now,” LaRoche said. “I think I did take a few steps backwards. That’s part of what today is, to try to get it back closer to where we need it. It’s not going to be a miracle. I’ve got a feeling that it’s probably going to be something that I’ll have to deal with for a while.”

Manager Jim Riggleman spoke with LaRoche today and told him, “I want 600 at-bats out of you.” He plans to rest LaRoche, 31, every now again, usually against left-handed starting pitchers. (The issue there, because of the Nationals’ dearth of right-handed bench bats, is that the Nationals will be forced more often against lefties to start Rick Ankiel, who in his career has hit .234/.285/.386 against lefties.) LaRoche insisted he would have played tonight if the Mets had a right-handed starting pitcher.

LaRoche said he will not require surgery during the season and will likely be able to heal his shoulder with only extensive rehab in the offseason. LaRoche is not concerned about the specter of a trip to the disabled list, but “that would change if I start feeling it in my swing,” LaRoche said. “That would be something that I can’t play through. That would be the worst case.”

As of now, “it still does not hurt to swing at all,” LaRoche said. LaRoche still takes a full complement of batting practice daily.

But throwing pains him. The Nationals signed LaRoche to a two-year, $16 million contract largely because of his excellent defensive ability, and he’s had to change the way he throws. LaRoche says he sometimes “short-arms” throws instinctively in order to mask the pain.

Tonight, Michael Morse will play first for LaRoche. Morse has played 37 games at first base in his career, 12 of them as a starter.