Sue Bird scored 25 points on Tuesday and the Storm dispatched the Mystics, 79-71.
Ann Wauters added 14 points for Seattle, which never trailed in the contest and led by as many as 14.
Crystal Langhorne had 20 points and 10 rebounds to pace the Mystics, who fell to 2-9 on the season. Monique Currie scored 15 in the setback.
The Storm were in front for the entire first half, but Washington battled back to tie the game on Currie's three-pointer near the midway point of the third quarter.
The Mystics failed to take the lead, however, and Seattle was up 55-47 by the end of the third courtesy of two free throws from Tina Thompson in the final minute of the quarter.