The Mystics (8-12) snapped a three-game losing streak as Emma Meesseman collected 12 points and 12 rebounds while Kia Vaughn added 10 points.
The Sky (8-11) dropped their third straight despite Sylvia Fowles' 19 points and 17 rebounds. Chicago rallied from a 13-point deficit to pull within five following Fowles' free throw with 2:41 left, but never got closer.
Epiphanny Prince scored 14 points, Jamierra Faulkner had 13 and Jessica Breland added 10 while Tamera Young had 12 rebounds for Chicago.
The Mystics beat the Sky for the second time this season.
The Sky are still playing without Elena Delle Donne, who is suffering from symptoms of Lyme Disease.
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