WASHINGTON -- Nationals reliever Ryan Mattheus, who is on the disabled list because of a sore shoulder, played catch and threw a bullpen session on Sunday.

The right-hander threw 25 pitches -- fastballs and breaking pitches -- without any problems.

The Nationals are hoping that Mattheus will be ready to pitch in a big league game by Sept. 20. In the meantime, Mattheus will play catch again on Monday in New York before throwing another bullpen on Tuesday.

"There is not going to be anything holding me back from getting back out there," Mattheus said. "I don't know how many innings it will be, but I think I'll be out there pretty soon."

Before getting injured, Mattheus was one of manager Davey Johnson's reliable relievers, going 2-2 with a 2.40 ERA in 32 games.

Peacock on track for first big league start

WASHINGTON -- Right-hander Brad Peacock is expected to make his first Major League start on Wednesday, which means left-handers Tommy Milone and John Lannan will be pushed back a day.

Milone will face the Mets on Thursday afternoon, and Lannan will face the Marlins at Nationals Park on Friday.

Peacock threw a bullpen session on Friday, and another one on Sunday.

"I'm excited," Peacock said about making his first Major League start.

Peacock last pitched on Tuesday, the same day that Stephen Strasburg made his season debut. Peacock pitched 1 1/3 innings, allowing a run on four hits in a 7-3 loss to the Dodgers.

"That was unfair to begin with," manager Davey Johnson said about Peacock pitching in relief. "I think we are going to have a start [for him] in about three or four days."

Peacock went a combined 15-3 with a 2.39 ERA and 177 strikeouts in 25 games with Triple-A Syracuse and Double-A Harrisburg this season. The 23-year-old ranked high among all Minor League pitchers in wins (tied for second), strikeouts per nine innings (sixth, 10.86) and strikeouts (seventh).

Johnson confident Espinosa will find stroke

WASHINGTON -- Entering Sunday's action, Nationals second baseman Danny Espinosa had struck out 11 times in his last 14 at-bats, but manager Davey Johnson was not worried. The skipper pointed out that the Espinosa has been trying too hard and needs to relax.

Johnson said Espinosa reminds him of when Phillies great Mike Schmidt first entered the league in the early 1970s. Schmidt didn't hit for average and struck out a lot.

"[Espinosa] is so driven. He is over trying. He is trying to do too much," Johnson said. "I kind of let him play his way out of it. He is too good a talent. I've been talking to him lately, but I know how driven he is. He takes great care of his body, he is tremendously strong, he watches too many videos, he studies the game. He is a special player.

"I'm not comparing him to a home run hitter like Mike, but Mike was driven like that -- obsessively. [He was] looking at everything, trying to do everything to be better until he learned to kind of step back and not try to do so much."

Johnson said that he and Espinosa were the last to leave the stadium Saturday night. There was Espinosa looking at video of himself playing in Double-A Harrisburg. Johnson told him to put a halt to watching the video and relax.

"I told him, 'Forget about all this stuff. You just need to relax a little bit,' We had a nice little conversation. He expects so much out of himself," Johnson said.

The conversation worked, as Espinosa had two doubles and scored a run in four at-bats against the Astros on Sunday afternoon.

"[Johnson] said, 'Don't press. I'm trying to do too much. Go out there and let your natural ability take over and just play the game,'" Espinosa said.