TUKWILA, Wash. (AP) — Before the season began, Seattle and Los Angeles were two of the most popular picks in the Western Conference to play for the MLS Cup title.

By the end of Wednesday night, one of those teams will have their season ended in the knockout round of the playoffs.

The star-studded matchup between the Sounders and Galaxy highlights the opening of the MLS playoffs. D.C. United will host New England in the Eastern Conference, while Seattle and Los Angeles play the nightcap out west on Wednesday.

On Thursday, Toronto and Montreal clash, followed by Portland hosting Sporting Kansas City.

The top two seeds in each conference — New York Red Bulls and Columbus in the East, and FC Dallas and Vancouver out West — received byes through the knockout round and will open the postseason on Sunday.

Seattle and Los Angeles have a lengthy playoff history even if the Sounders have only been around since 2009. Los Angeles has ended Seattle's season in the playoffs three times in the past six seasons and twice in the Western Conference finals.

Last year, Seattle won the Supporters' Shield for having the most points in the regular season and had home-field advantage in the two-game conference finals, but was ousted by the Galaxy because of a road goal by Juninho in the second half of the second game in Seattle.

Getting past the Galaxy in the postseason is the one obstacle Seattle has been unable to overcome.

"That's the reality of it. That's the current label. It is what it is. They obviously have our number in big, big games and that's the playoffs over the course of the last seven years it seems," Seattle captain Brad Evans said. "For us we have to try and rewrite the script."

It's been a weary couple of weeks for the Galaxy, who played a CONCACAF Champions League match in Guatemala last week, traveled to Kansas City for the regular-season finale on Sunday and now head to Seattle.

And there's no matching the star power that'll be on the field Wednesday night with Clint Dempsey and Obafemi Martins for Seattle and Robbie Keane, Steven Gerrard, Giovani Dos Santos and Omar Gonzalez for the Galaxy.

Here's a look at the other knockout round matches:

EASTERN CONFERENCE

(4) D.C. United vs. (5) New England, 7:30 p.m. EDT, Wednesday

New England was last year's representative from the Eastern Conference in the MLS Cup final but enters the playoffs this season on shaky footing. The Revolution snapped a four-match winless streak beating New York City FC in the regular-season finale on Sunday and is led by Lee Nguyen, an MVP candidate last year, and U.S. midfielder Jermaine Jones.

D.C. United will be testing the theory that regular season form means nothing in the playoffs after spending four months in first place in the Eastern Conference, only to drop points late losing three of its final five matches. D.C. was routed 5-0 by Columbus on Sunday.

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(3) Montreal vs. (6) Toronto, 7:30 p.m. EDT, Thursday

Montreal was struggling at midseason but the signing of Didier Drogba was the start of the Impact's turnaround. Montreal got 23 points from its final 11 games, Drogba scored seven goals in seven games and the Impact charged into the postseason.

Toronto is in the postseason for the first time in franchise history and has scoring firepower with Golden Boot winner Sebastian Giovinco, and U.S. stars Jozy Altidore and Michael Bradley. But Toronto was a sieve defensively, giving up 58 goals this year.

WESTERN CONFERENCE

(3) Portland vs. (6) Sporting Kansas City, 10 p.m. EDT, Thursday

Portland might be the hottest team in the MLS going into the playoffs. The Timbers won their final three games and scored 10 goals in the process to land in the postseason with a home game. Nigerian striker Fanendo Adi scored a franchise-record 16 goals this season, including four goals during Portland's three-game win streak to close the season.

Kansas City assured itself a spot in the postseason for the fifth straight season thanks to a 2-1 win over Los Angeles in the regular-season finale and has shown an ability to play up to its competition. Kansas City is unbeaten against Seattle, Portland and Vancouver this season.