Stefan Frei's goalkeeping heroics allowed Roman Torres to convert the winning penalty in the shootout and earn Seattle Sounders a first MLS Cup win at the expense of Toronto FC.

Both sides were contesting their maiden MLS Cup final and nerves seemed to play a part in a scrappy affair that ended 0-0 after 120 minutes of largely turgid fare at BMO Field on Saturday.

It was perhaps a profound statement that the one true moment of quality came from a keeper - Frei producing a stunning one-handed save to deny Jozy Altidore's header in the second half of extra time.

Frei, who spent four years at Toronto before moving to the Sounders, then saved from Michael Bradley in the shootout, before Justin Morrow hit the crossbar for Toronto, which allowed cult hero Torres to sweep home the winning kick to seal a 5-4 shootout success.

Toronto, roared on by a raucous home crowd, had much the better chances throughout the game, with Altidore and top scorer Sebastian Giovinco guilty of wasting their best opportunities before Frei's heroics in extra time and the shootout.

Altidore had netted in all five of Toronto's playoff games prior to the final and he went agonisingly close to maintaining that run when he shot narrowly wide after linking up with Giovinco as early as the second minute.

Toronto continued to press for an opener, Frei getting down to his left to keep out Altidore's header on the half-hour.

The second period started in much the same fashion as the first, with the hosts wasting a gilt-edged opportunity - Giovinco lashing an effort into the side netting from close range.

Altidore had one more chance to clinch it in normal time, but his header was smothered at point-blank range by Frei as the Sounders survived to reach an extra 30 minutes.

Toronto substitute Tosaint Ricketts - on as a replacement for a fatigued Giovinco - volleyed narrowly wide early in the second period of extra time, before his cross was headed goalwards by Altidore, who could scarcely believe seeing Frei claw it out of the top corner.

In the shootout, Frei denied captain Bradley, whose blushes were spared by Clint Irwin saving from the Sounders' Alvaro Fernandez, the score reading 4-4 after five kicks apiece.

However, full-back Morrow saw his kick crash off the underside of the bar, leaving Torres to convert and spark wild celebrations among Sounders players and fans alike.