WASHINGTON — The Montreal Impact wasted little time setting the tone against D.C. United when defender Laurent Ciman provided the lead just four minutes into the game.

From there, Montreal’s midfield took over and its top playmakers had one of their most dominant performances of the season.

Matteo Mancosu added a pair of goals and the Impact completely dominated D.C. United for a 4-2 victory in the knockout round of the MLS Cup playoffs Thursday night.

Ignacio Piatti also scored for Montreal, which hosts the New York Red Bulls in the Eastern Conference semifinals on Sunday. The Red Bulls won the regular season series 2-1 with both victories coming at home.

"We knew that D.C. was playing well, they have a lot of confidence and rhythm scoring goals at home," Montreal coach Mauro Biello said. "It was important for us to establish our shape early and not give them space. We were able to control different moments of the game with our midfield."

Montreal forward Didier Drogba, who scored 10 goals in 22 games this season, was not in the lineup because of a back injury. However, Drogba posted on social media that he attended the game, noting that he was a few minutes late because of traffic around Washington, D.C. area.

Drogba has a chance to get back in the lineup against the Red Bulls, according to Biello.

"The game Sunday could be more realistic for him," Biello said. "If he’s healthy, he will be available."

The Impact pressured D.C. United early and that proved to be an effective game plan. Ciman was unmarked inside the penalty and one-timed a cross from Marco Donadel’s corner kick for a 1-0 lead.

"If you give up a goal against them, you’re in trouble." D.C. United coach Ben Olsen said. "Because they counterattack as good as anybody in the league."

Mancosu received the most attention from the defenders as the sole striker and embraced that role. Mancosu got behind D.C. United’s defence in the 22nd minute on a headed pass by Donadel, but his low shot to the far post rolled just wide.

Even with the lead, the Impact continued to attack, which kept D.C. United out of sync and mired in its defensive third of the field.

Defender Hassoun Camara ran past a defender inside the penalty area in the 37th minute but he could not get his shot on goal. However, Mancosu did not miss five minutes later when he scored from close-range on a cross from Piatti for a 2-0 lead.

"I am feeling a little tired," Mancosu said through a translator. "I’ll take two days to recuperate well and be ready for Sunday."

The Impact outshot D.C. United 9-5 in the opening half.

D.C United pushed more players forward after the break and nearly cut the margin on a full volley by Nick DeLeon in the 49th minute. Montreal played more conservatively in the second half with 10 players behind the ball and relied mostly on counter-attacks.

"We knew when they were down 2-0, it was going to be hard for them," Donadel said.

Mancuso added his second goal on a cross by Ambroise Oyongo in the 58th minute. Mancuso, who came to the Impact on loan from Italian club Bologna in July, has five goals in 16 games with the Impact.

"He was fantastic," Biello said about Mancuso. "He brings experience to our team and he’s really found his rhythm and has adapted well to the team."

D.C. United’s best chance came in the 64th minute when Rob Vincent got one-on-one with Impact goalkeeper Evan Bush, but his shot hit the side of the net. From there, though, the Impact stayed in full control and Piatti added his team’s fourth goal in the 83rd minute.

D.C United finally got on the board in the final minutes on goals by Lamar Neagle and Taylor Kemp that gave the sparse crowd of 12,773 a reason to cheer.

Montreal and D.C. United tied 1-1 in both of their regular season meetings.