Tayler Hill tied a career-best with 16 points and Ivory Latta matched her. The victory made Mike Thibault the winningest coach for the Mystics (6-3), reaching 39 wins in his third season.
Elena Delle Donne scored 26 points to lead Chicago (5-4), which had a three-game winning streak snapped. The former Delaware star, who is averaging 29 points a game, sank all eight of her free throws and has made 48 straight. She's two short of her own mark set last year and 18 off the league record held by Eva Nemcova according to information provided by the WNBA from the Elias Sports Bureau.
She's 81 of 83 (98 percent) for the season.
Cappie Pondexter and Allie Quigley added 10 each.
The Mystics hit 10 of their 19 3-pointers and shot 50 percent from the field. The Sky missed all eight of their 3-point attempts.
Washington led as many as 20 after Latta's 3-pointer with 2:38 remaining in the third quarter. The lead never went under double digits thereafter.
Thibault passed Julie Plank's 38 victories.