It was Harper's first professional game since he played in the Arizona Fall League, where he hit .343 with a home run and seven RBIs in nine games for the Scottsdale Scorpions.
Harper entered the game against the Mets in the fifth inning as a pinch-runner for designated hitter Matt Stairs, who singled to right field to drive in Ian Desmond. Harper was able to get as far as second base before the inning ended.
Harper remained in the game as the Nats' DH and received his first at-bat in the seventh, striking out on three pitches against left-hander Taylor Tankersley.
2010 Spring Training - null
Sights & Sounds
Spring Training Info
In the ninth, Harper fanned against right-hander Ryota Igarashi on a curveball.
"I'm very pleased with what I saw [from Harper] and how he conducted himself," hitting coach Rick Eckstein said. "He is going to be fine. His mentality is to be aggressive. There are times when you are attacking the ball and your front side tends to leak a little bit.
"He is in the process of knowing what he needs to do. But he was really amped up today. He was real excited. There are things that we talked about on the bench that we are going to get back to."
Harper said he wasn't nervous at the plate, but agreed with Eckstein that he had some mechanical issues in both at-bats.
"I knew what [pitches were] coming. I pulled my front side a little bit in both at-bats," Harper said. "The first at-bat, I saw three sliders, but I felt really good. It's the first two at-bats in Spring Training. And I have a long way to go."
Riggleman said that Harper will enter Tuesday's game against the Mets as a defensive replacement for right fielder Jayson Werth, who will make his Nationals debut at Space Coast Stadium.
Riggleman is still not sure if Harper will start in an exhibition game, because the skipper wants outfielders Roger Bernadina, Michael Morse, Jerry Hairston Jr. and Rick Ankiel to get as many at-bats as they can before the regular season starts on March 31 against the Braves.
But the way he was talking after the game, Harper's days in big league camp are numbered. He has not been told if he is going to start the season in the Minor Leagues.
"I'm going to get my hacks in. I'm only going to be down here for a couple of more games," Harper said. "To get live at-bats on live Major League pitching is great. ... I'm going to try to get better as much as I can, get as many at-bats as I can and stay up here as long as I can. I think Major League pitching is going to make me a lot better. Like I said, I felt really comfortable up there and I love the atmosphere."
How is Harper going to remember his Spring Training debut?
"Two K's," he said. "That is going to stick with me probably until tomorrow morning, when I take my first hacks."
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.