The Phillies touched their former teammate for seven hits as Hellickson walked two to go with four strikeouts.
The Nationals activated Hellickson prior to the game, sending reliever Sammy Solis to Triple-A Syracuse.
Hellickson was 2-0 with a 2.28 ERA in nine starts entering the game. The veteran right-hander had been sidelined since June 4 with a right hamstring strain. He was 6-5 for Philadelphia last season.
Solis is 1-1 with a 4.50 ERA in 40 games this season. In 28 innings, the left-hander has allowed 22 hits with 30 strikeouts and 15 walks.
Also, Washington transferred third baseman Ryan Zimmerman, who has been out since May 10 with a strained right oblique, to the 60-day DL.
The Nationals reinstated catcher Raudy Read from the restricted list and optioned him to Triple-A Syracuse. Read, who appeared in eight games last season, is coming off an 80-game suspension after testing positive for a performance-enhancing substance.
Information from The Associated Press was used in this report.