Kayla McBride added 14 points, Angel McCoughtry scored 13 — including nine in the fourth quarter — and Dearica Hamby had 12 points and 13 rebounds for Las Vegas (3-2).
Emma Meesseman had season-highs of 24 points and 13 rebounds for Washington. Myisha Hines-Allen added 18 points and 10 boards and Leilani Mitchell scored 11 points.
McCoughtry hit a 3-pointer to give Las Vegas the lead for good 30 seconds into the fourth quarter and spark a 7-0 spurt that made it 67-61 when she made a jumper about 90 seconds later. The Aces made 9 of 10 from the free-throw line in the closing minutes.
The defending champion Mystics (3-2) have lost back-to-back games after winning three straight to open the season.