With 2009's No. 1 overall Draft pick Stephen Strasburg on the mound, 2010's No. 1 overall pick will start in left field as the youngest player -- at 19 years old -- to ever don a Nationals jersey.
The left-handed-hitting Harper, rated No. 2 by MLB.com's Jonathan Mayo, will get his first big league cuts against Dodgers righty Chad Billingsley, who was hit hard in his last time out.
Harper's callup comes on the heels of news that third baseman Ryan Zimmerman is headed for a DL stint because of his shoulder injury. To replace Zimmerman's bat in the lineup, Harper was called up -- the irony being that it was Zimmerman who previously held the mark as the youngest to play for Washington.
"We can use the left-handed bat in Harper," Nats manager Davey Johnson said. "I'm going to put him in left field and let him play. So he was a natural pick. He has been swinging the bat well."
Harper was hitting .250 with a homer and three RBIs for Triple-A Syracuse, but general manager Mike Rizzo spent the last three days in Syracuse, and said he's been impressed with Harper's bat.
The winner of Saturday night's game will claim the best record in the National League, as the two clubs are currently tied atop the senior circuit at 14-6.
For the Dodgers, Billingsley was sharp in his first three starts of the season, giving up just three runs. However, he had a tough time against Houston on Sunday, allowing nine runs (five earned) in just 3 2/3 innings.
"It's tough to pitch when you're not getting ahead of hitters and not throwing strikes," said Billingsley, who threw 33 balls during his 72-pitch outing. "One of those days you try to forget. You try to grind though it. I couldn't grind that long. I'm glad we got this game out of the way. It's a long season. In baseball, you have to have a short-term memory."
Dodgers manager Don Mattingly said Billingsley's poor start had nothing to do with a sore groin muscle that bothered him in his previous start against Milwaukee.
Nationals: Zimmerman eager for Harper's arrival
Zimmerman is eager to see how the newest National will fare at the beginning of his career. Most importantly, Zimmerman believes Harper's arrival gives the Nats a better chance to win games.
"Bryce is a very talented player. He can help us win," Zimmerman said. "He is someone we want on our team. He can help us in a lot of ways."
Strasburg has been dominant this season, posting a 2-0 record and a 1.08 ERA in his four starts.
Dodgers: Eovaldi in Dodgers' bullpen
The Dodgers recalled right-hander Nathan Eovaldi from Double-A Chattanooga, and optioned lefty Michael Antonini to Triple-A Albuquerque on Friday.
"This is something we had planned from the beginning," manager Don Mattingly said. "Because Atlanta was a lefty-heavy ballclub, Antonini made sense then. We see Eovaldi being up here for the short term."
In 13 Double-A innings this season, Eovaldi allowed three runs, while striking out 14.
Matt Kemp and Andre Ethier continue to trade the league's RBI lead back and forth. Friday night, Ethier re-claimed it with a two-run homer that put him at 24 to Kemp's 23. The club record for April RBIs is 29 by Ron Cey in 1977.
Billingsley is 4-1 all-time with a 3.21 ERA against the Nationals.
Kemp, who continues to garner MVP chants when he bats at Dodger Stadium, leads the league in average, home runs, on-base percentage and slugging percentage.