Photo by Joe Nicholson/USA Today Sports

SEATTLE — It took a tired, listless, and shorthanded opponent, but the Seattle Sounders finally looked a semblance of themselves on Sunday night, cruising to a 3-1 win over Real Salt Lake and qualifying for the playoffs in front of 55,435 at CenturyLink Field.

The Sounders scored three goals in the first 20 minutes and never looked back. Clint Dempsey provided an early brace and also assisted on Marco Pappa’s insurance goal.

Luis Gil pulled one back for Real Salt Lake in the 77th minute, finding himself unmarked on a softly-rolled cross from right back Tony Beltran.

The Sounders will host the LA Galaxy in the single-game knockout round either Wednesday or Thursday night.

With the win, the Sounders averted a devastating end to a roller-coaster 2015 campaign. The best team in the league for the first three months of the season, Seattle then lost nine of 11 matches over the summer before grinding out results — if nothing approaching peak form — down the home stretch. They entered Sunday’s match capable of finishing anywhere from second place to seventh place and out of the playoffs for the first time in club history.

Already eliminated from the playoffs, the visitors did not provide the stiffest competition in a match played mostly for pride and job security. Real Salt Lake qualified for the CONCACAF Champions League quarterfinals with a midweek win over Guatemala’s CSD Municipal, and the lack of rest and perhaps motivation showed. They were also missing goalkeeper Nick Rimando (injury) and captain Kyle Beckerman (accumulation), among others.

To the surprise of no one who has watched the Sounders this season, a big night from the oft-dynamic duo of Obafemi Martins and Clint Dempsey fueled Sunday’s win.

Dempsey opened the scoring in just the fifth minute, sliding into a short cross from Martins and poking the ball into the back of the net from mere feet in front of goal.

Dempsey then assisted on a beautiful long distance strike from Pappa, who buried a shot into the far corner of the net from the side of the arc.

Stepping into a rebounded Obafemi Martins shot on the counter, Dempsey finished into an empty net to cap the Sounders’ scoring in the 20th minute.

With the loss, RSL ends a disappointing 2015 season on a three-game losing streak in league play, out of the playoffs for the first time since 2007.