SEATTLE - Nicolas Lodeiro scored twice and Nelson Valdez added a goal - all in an 8-minute span early in the second half- and the Seattle Sounders rolled past FC Dallas 3-0 on Sunday night in the first leg of the MLS Western Conference semifinals.

Dallas, winner of the Supporters Shield with the best regular-season record, now must score at least three times when the teams play the second leg in Texas next Sunday to keep its season alive.

Valdez, whose 88th-minute goal beat Sporting Kansas City in a knockout game Thursday, put Seattle on the board in the 50th minute. Joevin Jones crossed a target ball from the left side into the penalty area. Valdez ran to the top of the 6-yard box, went up and over Dallas defender Maynor Figueroa and headed it into the back left corner.

Lodeiro made it 2-0 at the outset of the 55th minute, running onto Jordan Morris' short crossing pass and blasting it into the back right corner from 6 yards in front.

Just 3 minutes later, Lodeiro took a through ball from Jones, streaked down the left side, and, from the top left corner of the 6, fired to the far corner.

Nico scores his second and the #Sounders lead it 3-0: #SEAvDAL

— Seattle Sounders FC (@SoundersFC) October 31, 2016

Sounders have a significant leg up on Dallas heading into the second West Conference Semifinal game. The winner of the series is determined based on the total number of goals scored between the two games. Read more about MLS playoff rules.

Photos: Sounders vs. FC Dallas