Brenden Aaronson and Ilsinho also scored for the Union (14-8-6, 48 points), who moved level with Atlanta United -- who won on Friday -- in points atop the Eastern Conference standings.
D.C. (10-10-9, 39 points) played without leading scorer Wayne Rooney, who was suspended for the match after receiving a red card for a forearm to an opponent's head in Wednesday's 2-1 defeat to the New York Red Bulls. United lost for the fifth time in their past seven matches (1-5-1) and have scored just five goals in that span.
- Major League Soccer standings
- Timbers, Sounders fan groups protest silently
- Alright, alright! Matthew McConaughey owns new MLS team
It was the second time Philadelphia has routed D.C. this month. The Union won 5-1 in the nation's capital on Aug. 4.
Przybylko, who has a team-leading 12 goals, opened the scoring in the fifth minute. Aaronson and Kai Wagner played a nifty give-and-go down the left wing before Wagner sent a cross to the near post. Przybylko was able to get his left foot on the ball about 3 yards out and deflect it into the upper left corner of the net past D.C. goalkeeper Bill Hamid.
Aaronson made it 2-0 in the 16th minute, getting open to take a pass from Przybylko about 25 yards from the goal in the middle of the field. Aaronson dribbled the ball to the top of the 18-yard box before unleashing a left-footed shot into the lower left corner of the net.
Przybylko found Ilsinho at the top right corner of the 18-yard box for the third goal, in the 36th minute. Ilsinho dribbled past one defender and took a quick shot from about 10 yards just before a second defender reached him, putting the ball in the left side of the net for a 3-0 advantage.
D.C. got on the board in the 56th minute, thanks to Luciano Acosta. The midfielder outmuscled a defender for the ball about 25 yards from goal and zig-zagged past two others before trying to flick a pass to teammate Paul Arriola.
The ball bounced off defender Jack Elliott and right back to Acosta, whose one-timer from the top left of the 6-yard box found its way under Union goalkeeper Andre Blake.
Blake made three saves, while Hamid stopped two shots.
Union roll over struggling D.C. United
Kacper Przybylko found the net and had a couple assists, in Phliadelphia's 3-1 win over D.C. United at Talen Energy Stadium.