Ariel Atkins' steal and fast-break layup gave Washington a 67-65 lead and Kristi Toliver made a baseline jumper on the Mystics' next possession. Delle Donne blocked a shot and made an up-and-under basket at the other end for a four-point lead.
A'ja Wilson was fouled on a putback and completed the three-point play with 30 seconds left to pull Las Vegas within 71-70. But Natasha Cloud dribbled down the clock and made a driving layup. Las Vegas missed a two-point shot and Tianna Hawkins secured it at the line.
Hawkins finished with 17 points for Washington (2-0) and Atkins, a rookie, scored 15. The pair each made three of Washington's eight 3-pointers.