Toronto FC are headed back to a third MLS Cup final in four years after beating defending champions Atlanta United 2-1 Wednesday in the Eastern Conference final in Atlanta.

Nick DeLeon's long-range blast in the 78th minute -- his fifth career playoff goal, broke a 1-1 deadlock and proved enough to end Atlanta's reign.

DeLeon seized upon a pass from Alejandro Pozuelo, turned at the top of the penalty area and fired past diving Atlanta keeper Brad Guzan for the game-winner.

Atlanta had got off to a flying start, sweeping forward from the kick off and taking the lead after only four minutes.

A speculative ball over the top from Ezequiel Barco allowed Pity Martinez to spring the Toronto FC trap.

The Argentine attacking midfielder advanced towards goal and then squared unselfishly for Julian Gressel for the simplest of finishes.

It almost got better four minutes later when again Toronto's defence was caught napping and Martinez burst clear after a long ball forward by Atlanta.

Martinez once again did everything right, surging into the area and drawing a clumsy foul from the covering Michael Bradley to win a penalty.

But there was to be no second goal for Atlanta after striker Josef Martinez's spot-kick was well-saved by Toronto goalkeeper Quentin Westberg.

Atlanta had barely had a chance to digest that disappointment before Toronto equalised, French winger Nicolas Benezet curling in a right foot shot from outside the area to beat Brad Guzan on 14 minutes.

"I have to say that today, it was resiliency," said Toronto coach Greg Vanney. "It wasn't beautiful soccer. It was hard. These guys just refused to give up."

Toronto will face the Seattle Sounders in the MLS Cup final on November 10  in Seattle.

The Sounders toppled Los Angeles FC, winners of the Supporters' Shield with the best regular-season record, 3-1 on Tuesday in the Western Conference final.

Toronto lost to the Sounders in the MLS Cup final in 2016 in a penalty shoot-out but avenged that defeat with a 2-0 victory in the 2017 championship match.