Jamierra Faulkner added 10 points as the Sky (12-16) won their second straight since Delle Donne returned from Lyme disease. She played 16 minutes after playing 10 in Wednesday's 87-74 victory over New York.
Chicago moved within a half-game of New York for the fourth and final Eastern Conference playoff spot. Washington maintained a hold on second place in the East.
The Mystics got within six points early in the fourth quarter, but the Sky later had eight straight for a 69-57 lead with 5:33 to play.
Emma Meesseman scored 17 points while Ivory Latta had 12 for Washington (13-15).
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