Since the league went to a two-game, aggregate-goals format for its conference semifinals in 2003, only three of 11 teams have lost the first game at home and gone on to advance by getting a victory on the road.
Trailing 2-1 after Saturday night's loss to the Timbers, the Sounders will be trying to become the fourth team to accomplish the comeback.
"We know we need to get a goal. I don't care if we get that goal in the first five minutes or the last five," Seattle coach Sigi Schmid said on Tuesday. "At the end of the day we need to win the game."
Knowing that they need a goal means the Sounders must be aggressive in pushing forward and getting chances, but be cognizant of their own defensive struggles and make sure they don't give one up to the Timbers. The Sounders must win by one goal to force extra time. A two-goal victory would advance Seattle to the conference finals, while a draw would be good enough for the Timbers to move on.
Getting chances in the first leg were not the problem for Seattle. The Sounders finished with 20 total shots, including five on goal. While Portland goalkeeper Donovan Ricketts made a number of key saves, there were opportunities the Sounders simply didn't put away. Both Eddie Johnson and Clint Dempsey had good scoring chances that they could not convert.
"The last game we ended up having more possession than I thought we were going to have against them. That's how the game played out for us," Schmid said. "Unfortunately, we didn't turn that possession in the first half into goals."
The optimism for Seattle comes from the amount of attempts they got on goal in the first game and that two of the three comebacks have come in recent seasons. Los Angeles lost 1-0 at home to San Jose in 2012 and then won 3-1 on the road to advance. In 2010, San Jose lost 1-0 at home to New York then rallied for a 3-1 win on the road. And in 2006, Colorado pulled off a 3-2 road win at Dallas then advanced after winning a penalty kick shootout.
All three of those teams were able to overcome a one-goal deficit and that makes Osvaldo Alonso's goal in the 90th minute so important for the Sounders. The late goal for Seattle made a comeback in Portland feasible, rather than seeming impossible. And because the MLS does not use road goals as the tiebreaker - as other leagues in the world do in two-leg series - the Sounders only need a one-goal victory to at least push the match an additional 30 minutes.
Seattle will go into the second-leg without forward Lamar Neagle due to yellow card accumulations, but are hopeful of having forward Obafemi Martins and defender DeAndre Yedlin both healthy enough to contribute some minutes. Martins has been out with a groin injury while Yedlin has an ankle injury.
"This is what it's about - playing in the playoffs," Dempsey said this week. "If you can't get up for these games, then you shouldn't be playing. It's an opportunity to go down there and try to do something special."