Salt Lake pulled above the Western Conference playoff cutoff line with the critical victory.
Bill Tuiloma scored a second-half goal for Portland, which had its five-match winning streak and six-match unbeaten streak snapped. The Timbers missed an opportunity to overtake Seattle for first place in the West, though the Sounders now have a game in hand after their scheduled Wednesday contest against the Rapids was postponed due to Colorado's ongoing coronavirus outbreak.
The Timbers scored a goal in their 11th straight match but could not generate enough offense to overcome the early two-goal deficit.
Martinez opened the scoring in the 11th minute. The ball bounced to his feet after Portland goalie Aljaz Ivacic misjudged a long ball on a save attempt and pushed it out to Martinez. From there, Martinez used a quick dribble toward the six-yard box and blasted the ball home inside the right post once he got a clear look at an empty net.
Kreilach made it 2-0 in the 26th minute. Left unmarked atop the 6-yard box on a corner kick, Kreilach latched onto the ball and blasted a right-footed shot over Ivacic and buried it in the back of the net for his eighth goal of the season.
Portland pulled a goal back in the 77th minute. Diego Valeri served up a free kick into the 6-yard box. Tuiloma leaped high to snag the ball and headed it just under the crossbar to cut the deficit in half.
RSL finished with a 13-10 advantage in total shots though Portland wound up with 52.7 percent of the ball possession. The Timbers and Salt Lake each put four shots on goal.