By Ridge Mahoney

With Adam Moffat unavailable and Ricardo Clark not at full fitness, the Houston Dynamo midfield may have trouble containing D.C. United despite holding a two-goal lead heading into the second leg of their Eastern Conference final series.

Only two teams have overcome a two-goal deficit in an MLS playoff series, yet D.C. United has the weapons and conditions to take a good shot at coming back despite trailing, 3-1.

The return of Dwayne De Rosario, the possible availability of Chris Pontius, and a depleted Dynamo midfield give United hope it can emulate San Jose in 2003 and Kansas City in 2004 when it hosts Houston Sunday (4 p.m. ET, NBCSN) at RFK Stadium in the decisive second leg. Those teams overturned two-goal deficits in the conference semifinals; the Quakes captured the MLS Cup that year and Kansas City reached the final.

“We can’t sit back. We have to be the aggressor,” said United’s Perry Kitchen during a conference call with reporters Thursday. He normally plays a holding midfield role but will likely look for opportunities to push forward and exploit a shorthanded opponent. “They are up 3-1, 2-0 – however you see it. If we sit back that plays into their hands so we have to get after them.

“But with that being said, the game is 90 minutes. We don’t have to go out and get two goals in the first 10 minutes so there is an amount of patience that plays into that, and we’ve discussed that. It’s not going to be easy but we definitely think it’s doable.”

The teams split their early-season meetings – United won, 3-2, at RFK on April 28, Houston took a 1-0 decision at home two weeks later – and D.C. lost the third game, 4-0, July 15 at BBVA Compass Stadium after losing keeper Bill Hamid to a red card in the 17th minute.

Hamid comes off suspension for the second leg but the availability of other players is a concern for both teams. There are injury issues to key players, with Houston’s central midfield and United’s attack the most pressing.

Moffat, whose acquisition from Portland midway through the 2011 season sparked the Dynamo’s run to the championship game, is sidelined with a concussion. The return of Clark in early July following a stint in Europe helped stabilized the middle, but he’s questionable with an adductor strain. Clark missed the first leg, as did attacker Calen Carr and defender Jermaine Taylor, who are also questionable for game two.

A sprained MCL has sidelined 2011 MVP De Rosario for nearly two months, yet he’s certain to play and might even start. The D.C. catalyst has been impressing his teammates in training sessions the past two weeks and with Pontius questionable (groin strain) and overlapping right back Andy Najar suspended, the presence of De Ro could be decisive.

“He’s looked good,” said Kitchen. “He definitely doesn’t look like he’s been out for as long as he has been. He’s been sharp, he’s back directing traffic and leading the guys. If he is healthy I definitely think he’ll play a part in the game.”

Though Houston Coach Dominic Kinnear has some critical selections in the middle of the park, his flank attackers will be keen to steal away and punch in a goal that would drop D.C. deeper into a hole. Both Brad Davis and Oscar Boniek Garcia can also drift inside to compensate for the absence of Moffat and possibly Clark to provide impetus up the middle if necessary. They combined for 12 goals and 18 assists even though Boniek Garcia didn’t join the team until late June.

“It creates a good balance for us,” said Kinnear prior to the start of the playoffs. “You can get Brad wide in good positions and that’s a positive for us. On the other side of it, with Boniek tucking inside, if you get the ball in good spots he can and he’s able to turn and run at the defense, that’s a good thing for us to have.

“I will say that both guys can hang wide and also tuck in the middle. Obviously Boniek is more of a slasher than Brad, but Oscar does cross a good ball as well.”

The probable target of those crosses is second-year forward Will Bruin, who posted 12 goals during the regular season and is tied for the playoff lead with four. Though defense is the focus as Houston sets up with a two-goal lead, United can’t take lightly the Dynamo’s scoring prowess through the air, especially on set plays.

“We’re going into the game thinking it’s 0-0, that it’s a must win for us,” says Bruin. “We’re going to keep attacking and try to create our own chances. That being said, we have to be smart and not get caught with too many numbers forward where they can hit us with a counter. We’ve been doing a lot of possession drills and I think that’s going to be a big part of the game on Sunday.”