The Canadian midfielder recorded three goals against his former team to give him nine total for the season.
A week after recording two goals in D.C. United's win over San Jose, De Rosario scored a hat trick Saturday night as his team salvaged a 3-3 draw against Toronto FC at RFK Stadium.
De Rosario scored the game-tying goal on a penalty kick in the 88th minute, three minutes after Danny Koevermans gave Toronto its first lead of the night.
Peri Marosevic and Julian De Guzman also scored for Toronto.
De Rosario, who was traded by Toronto to the New York Red Bulls earlier this year before winding up in D.C., was given the penalty opportunity after Austin Da Luz was dragged down in the box. He beat Stefan Frei to the low right for his ninth goal of the season.
The Canada international midfielder has scored six goals in his last six games since joining United, three of which have come against his former squads.