Rookie Nick DeLeon scored in the 88th minute to lift DC United a 1-0 victory over the New York Red Bulls and into the Eastern Conference finals of Major League Soccer's play-offs on Thursday.
United advanced 2-1 on aggregate after drawing 1-1 on Saturday in the opening leg of the semi-final tie.
"It's unbelievable," DeLeon said after delivering the winner in a match postponed from Wednesday because of heavy snow in the New York-New Jersey area already hammered by superstorm Sandy.
United will face the Houston Dynamo in the Eastern Conference final tie. The first leg will be on Sunday and the return will be on 18 November in Washington.
In the Western Conference on Thursday, Mario Martinez scored with nine minutes remaining to give Seattle a 1-0 victory over Real Salt and a berth in the conference finals against reigning MLS Cup holders the Los Angeles Galaxy.
Seattle advanced 1-0 on aggregate after playing Salt Lake to a goalless draw in the opening leg.
The Sounders will visit the Galaxy on Sunday for the first leg of the Western Conference finals, with the return leg on 18 November.