VIERA, Fla. -- Nationals right-handers Jordan Zimmermann and Chien-Ming Wang had bullpen sessions without pain Monday, while left-hander Ross Detwiler played catch on flat ground.

For Zimmermann, it was his first session of the spring after having Tommy John surgery last summer. He threw 15 pitches -- all fastballs.

The trainers wanted Zimmermann to throw at 50 percent, but he threw the ball as hard as he could after the session started. Pitching coach Steve McCatty scolded Zimmermann for going full bore, but the misunderstanding didn't stop McCatty from praising Zimmermann for the way he looked on the mound.

"Jordan threw the ball very good," McCatty said. "We were trying to rope him in. He wanted to let it go. Chien-Ming was next to me. He looked at me when he said, 'Gas.' Jordan feels great and threw the ball great."

Zimmermann is ahead of schedule in terms of making a comeback, but general manager Mike Rizzo told Zimmermann that he would not pitch in a game until August. That's OK with Zimmermann, who is grateful to finally pitch on a mound.

"It was a pretty big deal, I guess, to step on a mound [for the first time in] seven months," Zimmermann said. "I didn't know where my first couple of balls were going to go, but they were right around the plate. I wasn't all over the placed, so that's good."

Zimmermann will not have another bullpen session until sometime next week. In between, he will throw on flat ground.

A little more than a month after having hip surgery, Detwiler was seen playing catch in Space Coast Stadium. It marked the third time he threw the baseball on flat ground.

Detwiler was walking on crutches for most of Spring Training, but stopped using them last week. Detwiler is not expected to throw in a game until late May.

"The hip feels fine," Detwiler said. "I shortened my stride a little bit as a precaution. Other than that, everything feels great."

Detwiler will meet with Dr. Marc Philippon on April 14 to make sure the hip is 100 percent. Philippon performed the procedure on Detwiler in Vail, Colo., last month.

Wang continues to get stronger. He threw 45 pitches and will have another bullpen session on Wednesday. It's not known when Wang will play in a simulated game or Minor League game.

"He said he felt good, no problems," McCatty said.