The 26-year old helped the second-year club hammer TFC 6-2 at BMO Field with a long range strike in the 11th minute to make it 2-0 before burying another left-footer from outside the area just after the hour-mark making it 4-2 after Toronto had fought back.
Mapp had scored just two goals in the previous two seasons and last won the Player of the Week award back in Week 23 of the 2005 season.
He becomes the 11th different player from 11 different clubs to win the award so far this season.
2011 MLS Player of the Week winners
Week 11: Justin Mapp (Philadelphia Union)
Week 10: Jeff Parke (Seattle Sounders)
Week 9: Justin Braun (Chivas USA)
Week 8: Joao Plata (Toronto FC)
Week 7: Will Bruin (Houston Dynamo)
Week 6: Landon Donovan (LA Galaxy)
Week 5: Luke Rodgers (New York Red Bulls)
Week 4: David Ferreira (FC Dallas)
Week 3: Camilo (Vancouver Whitecaps)
Week 2: Javier Morales (Real Salt Lake)
Week 1: Omar Bravo (Sporting Kansas City)