Pontius claimed this week's award for United after scoring two goals in a 4-0 win over Vancouver Whitecaps FC.
The 24-year-old opened the scoring in first-half stoppage time after being set up by De Rosario, while he scored United's third goal of the match 20 minutes from time by reacting quickly to knock home a deflected shot from Stephen King.
The brace gives Pontius a career-high seven goals on the season, and also earns him a second Player of the Week award for his career.
The MLS Player of the Week award is selected each week by the North American Soccer Reporters. The group consists of members of online, print, television, radio media. More information can be found at soccerreporters.com.
2011 MLS Player of the Week winners:
Week 1: Omar Bravo (Sporting Kansas City)
Week 3: Camilo (Vancouver Whitecaps FC)
Week 4: David Ferreira (FC Dallas)
Week 5: Luke Rodgers (Red Bull New York)
Week 7: Will Bruin (Houston Dynamo)
Week 8: Joao Plata (Toronto FC)
Week 9: Justin Braun (Chivas USA)
Week 10: Jeff Parke (Seattle Sounders FC)
Week 11: Justin Mapp (Philadelphia Union)
Week 12: Jean Alexandre (Real Salt Lake)
Week 13: Steven Lenhart (San Jose Earthquakes)
Week 14: Bernardo Anor (Columbus Crew)
Week 15: Mike Magee (Los Angeles Galaxy)
Week 16: Joel Lindpere (Red Bull New York)
Week 17: Fredy Montero (Seattle Sounders FC)
Week 18: Mauro Rosales (Seattle Sounders FC)
Week 19: Sanna Nyassi (Colorado Rapids)
Week 20: Dwayne De Rosario (D.C. United)
Week 21: Dwayne De Rosario (D.C. United)
Week 22: Chris Pontius (D.C. United)