A day ahead of the first full-squad workout, Harper stretched with several other early arrivals, did some light throwing and moved to another field for batting practice.
Harper, taken in last June's draft and given a $9.9 million, five-year contract, was not allowed to speak with reporters. He was besieged by autograph seekers after his workout, which lasted roughly 90 minutes.
With fans lining the fence, he took roughly 40 swings and hit four home runs -- all to right field. Two of them splashed in the small pond just over the fence.
Nationals first base prospect Chris Marrero, who was in Harper's hitting group along with infielder Brian Bixler, had not met Harper until Monday. He said Harper did not appear to be nervous.
"There was nothing to be nervous about," Marrero said. "It's just practice."
Several coaches and executives watched, including Doug Harris, Washington's director of player development.
"He looks great," Harris said. "You saw it. There's really not a lot of words that need to go into this. He's extremely prepared. Looks like he's been taking care of business all offseason."
Former major league manager Davey Johnson, a senior adviser for the Nationals, recalled seeing Harper win a home-run hitting contest when he was just 15 years old. Johnson knew the kid would be special then. He liked not only Harper's bat speed and hand-eye coordination, but the maturity he displayed.
The key for Harper, Johnson said, will be to get adjusted to the life of a professional and to see different kinds of pitchers.
"I don't want to put any pressure on him, but I think by the time he's 19, he'll probably have an at-bat or two in the major leagues," Johnson said.
Washington minor league third baseman Steven Souza, who got a big hug from Harper, has been impressed with the way the 18-year-old interacted with fellow players. The two first met in Instructional League, and Souza said Harper could not have been a better teammate.
"He's handling it like a grown man," Souza said. "There's a lot of stuff that he has to do that a lot of other people don't. I mean, he has eyes on him when he's drinking a cup of water."
Harris and Nationals manager Jim Riggleman said they will wait to see how Harper performs to determine which minor league team he will be sent to, but it most likely will be Class A Hagerstown.
"We react to what he's doing," Riggleman said. "If he's dominating, you keep moving him through the system. If he hits a little hiccup somewhere, you slow him down. He's a special young player, but minor league baseball is tough. He'll get tested, believe me. We have every indication he's going to pass those tests."