After trying to labor through an ailment, Roldan limped off with a groin injury in the 31st minute while Marshall was stretchered off following a knee injury just nine minutes later.
The Sounders went into halftime trailing 2-1 after the Timbers came back from an early deficit.
Roldan started all 34 games during the regular season, playing all but seven minutes for the team. Marshall started 30 games and is a finalist for MLS Defender of the Year.
The second leg of their series against the Timbers looms on Nov. 8.