Bryce Harper's first day in the major leagues came with all the hype one would expect for the player dubbed "Baseball's Chosen One" when he was only 16 years old.

The No. 1 pick in the 2010 draft went 1 for 3 in his first game for the Washington Nationals, with a booming double, tiebreaking sacrifice fly in the ninth and a bullet throw from left field that nearly cut down a runner at the plate.

It wasn't enough to keep the Los Angeles Dodgers from winning 4-3 in 10 innings Saturday night on a homer by Matt Kemp, but it was an impressive debut for the 19-year-old.

Greeted by a large crowd of reporters in the visitor's dugout at Dodger Stadium before the game, Harper expressed how excited he was for his debut.

"I think once the lights are turned on and the fans get here, I think that's when my energy level's going to go through the roof. So I'm trying to be as mellow as I can right now," Harper said. "My dad told me: 'Just to go out and have fun. It's the same game you've been playing your whole life.'"

His promotion from Triple-A Syracuse came a little earlier than expected — third baseman Ryan Zimmerman was placed on the disabled list because of inflammation in his right shoulder, making room for Harper. And there he was, listed on the Nationals' lineup card: the No. 1 overall pick in 2010 was set to start in left field and bat seventh.

It didn't take long for him to make an impression. In the seventh inning, Harper lined a double to straightaway center field in his third at-bat for his first major league hit. He lifted a sacrifice fly to left in the ninth to break a 1-1 tie.

The Nationals' bullpen couldn't hold a two-run lead.

Harper grounded back to the pitcher in his first major league at-bat and flew out to left in the fifth.

He also made a perfect throw from left field in the bottom of the seventh that would have nailed the tying run at the plate, but catcher Wilson Ramos let the ball pop out of his glove.

"He seemed very relaxed," Nationals manager Davey Johnson said before the game. "I asked him if he had enough sleep, because he came in very late last night. But as strong and as young as he is, I'm sure he doesn't need any sleep. Basically, I told him: 'Glad to have you. Just relax and have fun.'"

Hype has followed Harper every step of the way. He appeared on the cover of Sports Illustrated, heralded as "Baseball's Chosen One" in June 2009.

He signed a five-year, $9.9 million contract with the Nationals in August 2010, a record for a non-pitcher signed out of the draft who had not become a free agent. The deal included $6.5 million in signing bonuses.

He progressed through the Nationals farm system rapidly, playing in Class A and Double-A last year and at Syracuse this season, where he was hitting .250 with a homer and three RBIs in 72 at-bats.

This spring there was talk about Harper making the Nationals out of spring training but he was sent to the minors for more experience.

"I talked to him about why he was going down to play, so that I won't have to answer these questions if he struggled up here about why he didn't get more seasoning. So we got that out of the way," Johnson said.

Harper, who doesn't turn 20 until Oct. 16, joined the Nationals with 142 games left in the season. There have been 17 players in major league history who have played at least 100 games as a teenager, including Mel Ott, Ken Griffey Jr., Robin Yount, Al Kaline, Ed Kranepool, Rusty Staub, Tony Conigliaro, Edgar Renteria and Jose Oquendo.

"I think they are very careful with the people they call up at a young age — because, obviously, getting to the big leagues and sticking is not guaranteed for anyone. So I think they took that into consideration," said Zimmerman, who made his big league debut at age 20, less than three months after the Nationals selected him fourth overall in the 2005 draft.

Of the 31 position players taken first overall in the draft since it began in 1966, only two hit home runs in their big league debuts. Atlanta third baseman Bob Horner did it in 1978 and Tampa Bay outfielder Delmon Young in 2006.

"The game is definitely faster up here. There's no denying that. But the best advice I could give Bryce is that baseball is baseball," Zimmerman said.

Harper, who has replaced Zimmerman as the youngest player to wear a Nationals uniform, made plenty of headlines and highlight shows while in the minor leagues because of his quick temper. His teammates are hopeful that his days of slamming helmets, getting in umpires' faces and getting himself ejected for arguing called third strikes are over.

"At first, Bryce had a different way of expressing his confidence. But from last spring training to this spring training, I've never seen someone grow up as much as he has in one year — just the way he carries himself and the way he thinks things differently now," Zimmerman said. "That's not to say that two years ago he was a bad person. I mean, Bryce is a great kid. He means well, works hard and plays the game the right way. So you'll never have to worry about him not playing hard."

Harper has played in a big league ballpark before. He participated in last year's All-Star Futures Game at Arizona's Chase Field, going 0 for 4 with two strikeouts.

"When young players come up here, there's a lot of pressure on them to perform and prove that they belong up there," Johnson said. "And sometimes when there's too much hype about it, the tendency is to try to do too much. Bryce is so driven, a lot of times he tries to do too much. But if he just stays within himself and does the things he's capable of doing, he'll be fine."