The Mystics (14-7) had their five-game win streak snapped.
Turner and Mitchell scored five points apiece during a 14-2 run that gave Phoenix a 60-41 lead late in the second quarter. Griner scored 23 points on 10-of-11 shooting in the first half.
The Mercury (11-10) shot a season-high 58.2% from the field and had 28 assists on 39 field goals. They tied their season high with 12 3-pointers and made all 13 free-throw attempts.