The reigning NL Rookie of the Year, who is 20, drove a pitch from Miami Marlins right-hander Ricky Nolasco over the out-of-town scoreboard in right-center in the first inning. Harper's second homer sailed a little to the right of that in the fourth inning.
That first homer made Harper the fourth-youngest player to go deep in his team's first game. Robin Yount was 19 when he homered for Milwaukee against Boston on April 8, 1975, according to STATS. Tony Conigliaro and Ken Griffey Jr. also were younger than Harper, who is 20 years, 167 days old.
Don Money was 21 years, 305 days old on April 8, 1969, when he hit two homers for the Phillies.
After Harper's second homer Monday, some fans at Nationals Park serenaded him with "M-V-P!" chants and he gave a curtain call, stepping out of the dugout and pumping his right fist.
It's the third multi-homer of Harper's career, second against the Marlins.
Harper was 19 when he was called up to the majors by the Nationals in April 2012, turning in one of the finest seasons by a teenager in baseball history. He finished with 22 homers, 59 RBIs and 98 runs scored.