"It's a pretty simple game, really," said Real Salt Lake coach Jason Kreis. "... You have to score goals to win games and, if you don't win games, you don't advance."
As the game crept toward overtime, the critical sequence started when RSL turned the ball over near midfield.
Seattle forward Fredy Montero lobbed a long pass over defender Tony Beltran to Martinez. He approached goalkeeper Nick Rimando from a right angle and powered a low drive into the far corner.
"He hit the ball very well," said Rimando. "In the offseason, I'm going to keep thinking how I could have saved that ball. But you've got to give credit to him and Seattle. They had a good game plan."
The loss was RSL's first in nine games, going back to the regular season. The team went the final 513 minutes without scoring.
"It's been a while since we scored," said midfielder Kyle Beckerman. "I miss celebrating. ... I think we put the pressure on them. We created a couple of chances that we needed to, and we didn't score."
Real Salt Lake's first opportunity came in the sixth minute, when Javier Morales dodged two defenders and was tripped from behind on the edge of the penalty area.
Morales' free kick was blocked, however, and his ensuing corner kick was headed out of danger by the defense.
In the 10th minute, RSL striker Alvaro Saborio's perfect pass gave midfielder Ned Grabavoy a chance from a tough angle.
Grabavoy struck his shot solidly, but Seattle keeper Michael Gspurning smothered it, preventing RSL from breaking into the lead.
Seattle converted an RSL turnover in the midfield into a splendid opportunity in the 30th minute.
After referee Chris Penso awarded the Sounders a free kick from 30 yards in front of Rimando, Martinez hit the crossbar.
But the ball bounced away, keeping the game scoreless.
In the second half, it took Seattle less than a minute to leave the partisan crowd of 19,657 gasping.
Finding himself alone at the top of the penalty area, midfielder Brad Evans launched a low rocket at the goal.
As he did throughout Game 1 of the series, however, Rimando saved RSL. He dove to his left and deflected Evans' shot just beyond the near post.
"Both goaltenders," said Kreis, "were incredible."
When Real Salt Lake routinely cleared the resulting corner kick, the danger passed at least until Martinez found himself alone against Rimando.
"I don't know the guy's name," Beckerman said. "But he pulled something out of the hat. Great strike, and they deserve to go on."
After Martinez scored, Real Salt Lake swarmed around Gspurning but could not score.
R Real Salt Lake fails to score in the two-game playoff series and sees its MLS season come to an end.
• Seattle's Mario Martinez gets a shot past Nick Rimando in the 81st minute.