Argentina's Lucas Melano scored in the fifth minute of second half stoppage time Sunday to give the Portland Timbers a 2-2 draw at FC Dallas and a berth in next Sunday's Major League Soccer Cup final.
The Timbers won the two-leg aggregate Western Conference final matchup 5-3 after taking the opener 3-1 at home last weekend.
Portland will face the Eastern Conference winner, either the New York Red Bulls or Columbus Crew, in the championship match. The Crew won the first leg at home 2-0 with the second leg set for later Sunday.
Nigerian Fanendo Adi opened the scoring for Portland in the 54th minute, but Dallas battled back on goals by American Ryan Hollingshead in the 68th minute and 34-year-old Panama striker Blas Perez in the 73rd minute.
Needing one more goal to level the aggregate, Dallas was denied to the finish with Melano putting the dagger in the Texans' hopes.
"A lot of teams would have given up the next goal but we didn't. That says a lot about this team," Timbers coach Caleb Porter said. "I couldn't be more proud of this group. It's a big moment for us and a big trophy but we want the biggest one."
Argentine midfielder Diego Valeri assisted on both Portland goals in the same stadium where he suffered torn knee ligaments last year.
"This is special for the team, the club and the people," Valeri said. "It was very difficult. They played really well.
They had chances. But we fight, we work and we got this win."
No MLS team has rallied from a two-goal deficit to advance on aggregate since Kansas City in 2004.