Hamdi Salihi added a second-half goal for United (7-4-3). The Washington club is unbeaten in its last seven home matches, including victories in the last four.
Danny Koevermans scored for Toronto, a loss away from tying the league record for the longest losing streak at any point in a season. Real Salt Lake lost 10 in a row in 2005.
De Rosario has scored three goals in his last five matches, and has four multi-goal games since D.C. acquired him in a trade last June with the New York Red Bulls.
He put United ahead in the first minute when he outraced Toronto's Ashtone Morgan and headed in Branko Boskovic's free kick. De Rosario doubled D.C.'s lead in the 43rd when he drove in Chris Korb's low cross after Josh Wolff played Korb down the right.
Toronto appeared to have new life in the 71st minute when Koevermans reached a long, straight free kick from Julian de Guzman and scored from close range. But Salihi struck 2 minutes later, reaching Andy Najar's cross after Najar eluded de Guzman and Jeremy Hall on the right.
Salihi, signed in the offseason from Austrian club Rapid Vienna, has four goals in his last five games after failing to score in United's first nine matches.
- Dwayne De Rosario
- Toronto FC
- Hamdi Salihi
- Danny Koevermans