The Sounders appeared on their way to a victory when Wallace, who came off the bench in the second half, got under a pass from Andrew Jean-Baptiste and knocked home an open header from 10 yards out for the equalizer.
The Timbers improved to 0-1-2 with the result.
Eddie Johnson scored in 13th minute for the Sounders (0-1-1) in the Cascadia Cup contest.
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