Matee Ajavon led the way with 16 points, and Washington took down New York, 66-57, on Friday.
Tierra Ruffin-Pratt scored 10 of her 12 points in the fourth quarter, while Crystal Langhorne clocked in with 14 and Ivory Latta added 11 with seven assists for the Mystics, who matched a season high with their third straight win.
Katie Smith had 14 points and Cappie Pondexter poured in 10 for the Liberty, who had taken the season's first two meetings with Washington.
The visitors sealed the win thanks to a quick burst in the fourth quarter, a 7-0 run to start the period which put them up 52-44 on a Ruffin-Pratt jumper.
Ruffin-Pratt struck again with roughly 4 1/2 minutes to play which gave Washington a 58-46 edge, and New York got no closer than eight for the remainder of the contest.