The conference semifinals open when the top-seeded Colorado Rapids host the fourth-seeded Portland Timbers at Dick's Sporting Goods Park.
Colorado earned the top seed in the West on the final day of the regular season with a win and dropped points by Seattle and Sporting Kansas City.
Portland defeated Minnesota United 3-1 in the first round to earn a spot in the West semis, where they will face the Rapids in the playoffs for the first time ever.
Team news
Keegan Rosenberry is likely to miss out due to an unspecified injury. Other than that, Colorado has a full squad to choose from.
Andy Polo (quadriceps/leg), Jeff Attinella (ruptured rectus femoris tendon) and Eryk Williamson (torn ACL in left knee) all remain out for Portland.
Predicted lineups
Colorado: Yarbrough; Trusty, Wilson, Abubakar; Acosta, Price, Warner, Galvan; Kaye, Rubio, Barrios
Portland: Clark; Bravo, Zuparic, Mabiala, Van Rankin; Paredes, Blanco, D. Chara; Asprilla, Mora, Y. Chara
Ones to watch
William Yarbrough (Colorado)
He was part of a stingy Rapids defense that allowed the second-lowest goals in the league (35). He played in all but one game, led all goalkeepers in wins (17) and tied for the MLS lead in clean sheets (13).
Sebastian Blanco (Portland)
He is the heart and soul of the club and lifted the Timbers past Minnesota with a second-half brace. How he performs in this one will be the key to the match.
Previous meetings
This is the third meeting of the season between Colorado and Portland.
In September, Blanco's stoppage-time equalizer rescued a point for the Timbers in a 2-2 draw.
Last month, goals either side of halftime by Dominique Badji and Diego Rubio gave the Rapids a 2-0 victory.
How to watch
The match will be nationally televised on FOX for English-language coverage and on FOX Deportes for Spanish-language coverage.
Kick-off is set for 4:30pm Eastern time.