“We know we have to be aggressive, we know we have to go after them,” D.C. United Coach Ben Olsen said, “but we also have to be patient.” (Ned Dishman/Getty Images)

In order to advance to the MLS Cup for the first time in eight years, D.C. United is going to need to score two goals Sunday — maybe more, if the club concedes any. In such a tight spot, the natural instinct is to throw players forward and attack without restraint.

Heading into the second leg of the Eastern Conference finals, however, United is taking a counterintuitive approach.

“We know we have to be aggressive, we know we have to go after them,” Coach Ben Olsen said, “but we also have to be patient.”

Patience has been the theme and virtue at practice all week. Olsen and assistant Chad Ashton have emphasized it repeatedly, cautioning players about trying to make up the difference right away in the total-goals series against Houston.

The Dynamo won the opener at home last Sunday, 3-1, and would advance to the Dec. 1 championship game against Los Angeles or Seattle with a victory, draw or one-goal defeat at RFK Stadium. If United wins by two goals, 30 minutes of overtime and, if necessary, a penalty kick tiebreaker would follow.

“We know what we have to do,” defender Dejan Jakovic said. “This is going to be the biggest game of a lot of our careers. It’s not a time to panic. We have to approach it cautiously and not go flying out.

“If it’s 0-0 in the 50th minute, relax, play our game, keep the ball. We know they are going to sit back and protect their lead. Chances are going to come. We feel confident we can get at least a couple of goals.”

Short-term and long-term history are working against United. Without injured star Dwayne De Rosario, the club has scored multiple goals in just one of its past nine matches. Houston has yielded more than one only once in eight outings.

Since MLS implemented two-game, total-goals format nine years ago, two of nine teams have overcome two-goal deficits after the first leg. In 2003, the San Jose Earthquakes lost at Los Angeles, 2-0, and then forced overtime with a 4-2 victory. They subsequently won in the extra period on a 5-4 aggregate. The next year, Kansas City responded to a 2-0 loss at San Jose with a 3-0 victory at home.

United has faced a two-goal series deficit once before, in 2003. D.C., the lowest seed, lost both legs to Chicago by 2-0 scores.

Both conference finals this year feature considerable margins: Seattle lost the Western opener to the Los Angeles Galaxy, 3-0, and will host Game 2 on Sunday night.

“We need to wear this team down, and the way we are going to do that is by possessing the ball,” D.C. midfielder Nick DeLeon said. “If we can do it over a long period of time, they’re going to get tired chasing us. That is when gaps open up and that is when we go at them. It’s just about being patient. I’m in no rush. Possession will kill that team.”

United likes its chances. The club has not lost at home since the season debut in March (12-1-5 overall) and is averaging more than two goals per game at RFK. Houston was 3-9-5 in regular season away matches, including a 3-2 loss in Washington in April.

In the postseason, however, the bottom-seeded Dynamo won a first-round playoff at Chicago, 2-1. And in the conference semifinals, despite a 1-0 loss at Kansas City in the second leg, Houston eliminated top-seeded Sporting on a 2-1 aggregate.

The Dynamo also is a disciplined, battled-tested squad that upset Kansas City on the road in the 2011 Eastern final and was level with host Los Angeles in MLS Cup before conceding Landon Donovan’s late goal.

“We’re certainly going to have to be a little bit more aggressive, but nothing really has to change,” Olsen said, a comment that suggests he will use standard tactics, at least in the first half, and refrain from starting extra attackers. “It’s not a thing where we need two goals in the first 20 minutes.”

United notes: Leading scorer Chris Pontius did some light work Thursday but remains questionable after injuring a groin muscle in Game 1. Defender Brandon McDonald (calf) and midfielder Marcelo Saragosa (knee) are further ahead in their recovery and seem likely to suit up Sunday.