The other two were Eddie Mathews and Mel Ott, who are both in the Hall of Fame.
The 21-year-old Acuña launched a two-run shot Thursday in the third inning, a towering 432-foot drive into the second level at SunTrust Park off Philadelphia's Aaron Nola.
With eight games left in the regular season, Acuña also has a shot at becoming just the fifth player in baseball history to hit 40 homers and steal 40 bases in a season. He has 37 stolen bases.
Mathews hit 47 homers as a 21-year-old for the Milwaukee Braves in 1953. Ott was 20 when he hit 42 homers for the New York Giants in 1929.
More AP MLB: https://apnews.com/MLB and https://twitter.com/AP_Sports
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.