Houston (3-1-0) at D.C. United (1-1-1), 4 p.m.

Washington, D.C. (Sports Network) - The Houston Dynamo completed an undefeated season at home in the first leg of the Eastern Conference finals, and will try to protect a two-goal lead Sunday in the second leg at D.C. United.

Houston opened BBVA Compass Stadium this season, and went unbeaten in 21 games in all competitions - 19 in league play including the postseason. Overall, the Dynamo are unbeaten in 30 straight in all competitions at home.

The challenge this week is to protect the advantage on the road, where Houston struggled during the regular season, but has done enough in the postseason as it tries to reach a second straight MLS Cup.

United will hope to continue it season-long turnaround at home, as it carries an 18-game home unbeaten streak into the return leg at RFK Stadium. But even a win will not be enough.

D.C. must win by at least two goals to force overtime - and possibly penalties - or three goals to win the series on aggregate. United has seven home wins by at least five goals, and Houston has seven road losses by at least two goals.

"In no way are we out of this," United coach Ben Olsen said.

While United will use its home-field advantage this week, the key to the match could come down to the health of both sides.

Leading scorer Chris Pontius remains questionable with a groin strain after he left the first leg early, and 2011 MLS MVP Dwayne De Rosario is probable after spending months sidelined with a sprained knee for United.

Olsen also has other injury concerns, and right back Andy Najar is serving the third game of his suspension for a red card in the conference semifinals.

United will need some bench players to step up if it hopes to reach its sixth MLS Cup final, which would be played at RFK should it win.

"These stakes we haven't had in a while. The beauty of it is we can score two goals, especially knowing that we need to score two goals," Olsen said.

D.C. will need players to step up offensively, as rookie Nick DeLeon has two of three goals - the other was an own goal - in three postseason matches this season.

"We can't sit back, we've got to press. RFK is a fortress, we always seem to be on top of our game there so I don't have any worries," DeLeon said. "I know we can win by two or more goals against this team."

Houston was without Calen Carr, Ricardo Clark and Jermaine Taylor in the first leg and they remain on the injury report this week. Adam Moffat left the first game with a concussion, and his status remains unclear.

But with the two-goal cushion thanks to goals from Andre Hainault, Will Bruin and Kofi Sarkodie, Houston is in position to sit back and defend its cushion, even without a few of its important players.

"We are halfway there. They are a great team and I think you saw that here," said Houston defender Bobby Boswell, who started his career with United. "They are going to have a whole week to recover and be ready and we need to make sure we are ready when we go to RFK Stadium."