TUKWILA — Getting over the disappointment of Sunday's playoff loss has been no easy task for Sounders FC.

"I'd be lying if I said it's not still affecting us," said forward Eddie Johnson. "We're all human. Feelings don't go away overnight."

Added defender Jeff Parke, "It's a discouraging, tough one to swallow."

Those emotions fit the reality of the daunting task the Sounders face in the second leg of the Western Conference finals against the Los Angeles Galaxy. Seattle is down 3-0 heading into Sunday's 6 p.m. series finale at CenturyLink Field. Only one team in MLS history has overcome a deficit of three goals or more to advance.

The 2003 San Jose Earthquakes, who conceded the first four goals in the conference semifinals to the Galaxy — led then by current Seattle coach Sigi Schmid — came back to win 5-4 on aggregate.

It's the stuff of legend the Sounders hope to repeat.

"So many stories have been written and so many good things have come from teams that haven't quit when they should've," Parke said.

"We all have to come together and realize we could do something special here. They could be talking about us for a while if we can come back and pull this off."

At a minimum, Seattle must earn a three-goal win in regulation Sunday. That would force a 30-minute overtime, and if there's still no winner, one would be settled in a penalty-kick shootout.

So how often have the Sounders won an MLS game by three goals? Ten times in 137 games, regular season and playoffs, since joining the league as an expansion franchise in 2009. Eight of those games came at home.

In the same time frame, the Galaxy has suffered five three-goal losses in 143 games.

The list shrinks further when the margin is four goals, which Seattle needs to advance to its first MLS Cup outright. The Sounders have four such wins in franchise history; L.A. has one such loss in the past four years — a 4-0 drubbing at CenturyLink Field three months ago.

"Sunday has the opportunity to be a fantastic evening for the club, for the league, for soccer," said Schmid, "but it's a deep hole."

Many Sounders have played down the significance of a four-goal win against the Galaxy this season, noting the circumstances are vastly different. And they won't need to draw on stats or history for motivation.

"The fact that we just got our asses kicked is motivation enough," said midfielder Brad Evans.

"Motivation just has to come from within."

NOTES

• Ticket sales for Sunday's game have exceeded 40,000 and sections of CenturyLink Field's upper deck have been opened, according to a team spokesman. The crowd will set a franchise playoff record and be the largest MLS postseason crowd for a non-final.

• D Leo Gonzalez (hamstring) has returned to practice after missing the past six games, though Schmid said game fitness remains a concern. MF Mauro Rosales (hamstring) is improving but hasn't rejoined full training yet.

Joshua Mayers: 206-464-3184 or jmayers@seattletimes.com