PITTSBURGH -- Washington first baseman Adam Dunn was out of the lineup for Saturday night's game in Pittsburgh. Michael Morse was inserted in Dunn's customary spot at first base.

"He's a little banged up," Nationals manager Jim Riggleman said. "Certainly it's a day off, but he's been playing with a bad hamstring. As I've mentioned many times, be it [Josh] Willingham or Ryan Zimmerman, Ian Desmond with his thumb and Pudge Rodriguez with some issues, these guys have been playing through a lot of aches and pains. Adam has been playing with a bad hamstring for about 10 days, so we're going to shut it down today. Hopefully we'll get him back in there tomorrow."

Espinosa bringing excitement since callup

PITTSBURGH -- Infielder Danny Espinosa's contract was purchased from Triple-A Syracuse on Sept. 1, and he has certainly made an impression in his first two appearances for the Nats.

He notched an RBI double in his Major League debut on Wednesday at Florida. Then in his first big league start on Friday in Pittsburgh, he hit his first home run and had his first multihit game.

"This is about him getting acclimated into the league, to see the pace of the game, see if there is anything different," Washington manager Jim Riggleman said. "For the most part, I think he's going to feel like he's comfortable and everything is the same, the talent is better, but hopefully by the end of the month he realizes that he's played enough to realize he can play here."

Espinosa, who has played second base with the Nats, is a natural shortstop, but he could be the team's starting second baseman next year, joining regular shortstop Ian Desmond as the double-play combination.

"I think both those guys are real credits to the organization and credits to our scouts and player development," Riggleman said. "Both spent significant time in the Minor Leagues. They are products of our scouting and our system. To have a shortstop and second baseman come through your system and implant themselves there -- hopefully for the long haul. It's too early to tell for sure, but they both are very athletic. We know they are Major Leaguers athletically, if they are Major League players we'll know that in time. It's pretty special to have two good athletes like that in the middle of your diamond."

Espinosa is batting .500 in two games with the Nats and has one home run and two RBIs. In a combined 123 games for Double-A Harrisburg and Syracuse this year, the 23-year-old hit .268 with 22 homers, 69 RBIs and 25 stolen bases.

"His style of play is that he's a high-energy guy," Riggleman said. "He's stealing bases, he's playing hard, he throws hard. The only guy I've ever seen, and I go back to Shawon Dunston's arm and Ian Desmond's arm, and this kid's arm is like that. We've got high-energy, throw-the-ball-hard, run-hard, swing-hard attitude to the game."

Riggleman plans to use Espinosa extensively down the stretch in this season.

"We've probably got 25 or 28 games somewhere in that range, and hopefully he'll be in there in 15 to 20 of those games," Riggleman said. "A considerable amount and actually could be in more if we get him a couple of games at shortstop. He's going to get a lot of action."

Olsen moved to 'pen; Maya to make debut

PITTSBURGH -- As expected, lefty Scott Olsen has lost his spot in Washington's rotation. His next turn to pitch was Tuesday against the Mets, but he will be moved to the bullpen. A baseball source confirmed that Cuban righty Yunesky Maya will make the start.

"Right now what we're going to do is put Olsen in the bullpen for the immediate future," Nats manager Jim Riggleman announced. "That would be his start on Tuesday. I have a pretty good idea who it's going to be, but we're not ready to announce that yet. Olsen will get some more starts as we go down the stretch, but Tuesday it's going to be somebody other than him."

Maya, who went 5 2/3 strong innings in his final Triple-A start, will be making his big league debut. He is ready to pitch in the Majors, and general manager Mike Rizzo wants Maya inserted into the Nationals' rotation.

Since he returned from the disabled list on July 29, Olsen is 1-6 with an 8.72 ERA, having allowed 45 hits in 32 innings.

"I think we want to see some other people start," Riggleman explained. "We do have a month left in the season to see if he can acclimate himself to the bullpen, but we do have some other guys who are going to be joining us in next few days who could make that start."

Worth noting

Nationals relievers have fanned 415 batters this season, eclipsing the 393 strikeouts recorded last season. Ian Desmond has batted a team-best .371 with 10 doubles, three home runs and 16 RBIs in the past 35 games beginning July 27. He has 15 multihit games, including six games with three or more hits. ... The Nats are 0-15-2 in their past 17 road series since going 2-1 in a three-game set at New York against the Mets from May 10-12.