United advanced 2-1 on aggregate after playing New York to a 1-1 draw Saturday and faces the Houston Dynamo in the conference final.
In a game that was postponed a day after a Nor'easter blanketed the field with snow Wednesday night, the Red Bulls appeared poised to take the lead in the 69th minute when they were awarded a penalty kick as D.C. United goalie Bill Hamid was given a red card.
In a wild series of events, the Red Bulls scored a goal that was taken back before D.C. backup keeper Joe Willis made a crucial save on the second attempt. Kenny Cooper put his initial penalty kick past Willis, but the goal was called off by the referee because the Red Bulls had entered the penalty area early.
Willis, apparently warmed up after the first attempt, dove to his left on Cooper's second penalty kick attempt and made the save. Cooper took a little hop before the shot, but decided to go to his right and was thwarted by Willis. His first kick had beaten Willis to the other side.
Robbie Russell's through ball sent DeLeon in on goal alone and he put his chance past Red Bulls keeper Luis Robles, who was hardly tested all game.
SOUNDERS 1, REAL SALT LAKE 0
SANDY, Utah (AP) — Mario Martinez ended a season-long scoring drought for the Sounders against Real Salt Lake when he found the net in the 81st minute, helping Seattle advance to the Western Conference finals after the teams played to a scoreless tie in the first leg of their series.
The third-seeded Sounders scored for the first time in five games against Real Salt Lake this season, including the semifinal opener last Friday in Seattle. With a 1-0 aggregate victory, the Sounders earned a trip to the conference finals against the Los Angeles Galaxy. The Galaxy defeated the San Jose Earthquakes.
Fredy Montero set the scoring play in motion when he swung a cross out to Martinez on the left side of the box. The pass drew Salt Lake goalkeeper Nick Rimando toward the left post. Martinez fired at the opposite post and buried the ball in the right corner.
Second-seeded Salt Lake became the third higher seed to be knocked out of the MLS Cup Playoffs. The Sounders had been winless in three games against RSL during the regular season after failing to score in any of them.