Tayler Hill added 18 points for Washington (10-6) and All-Star Stefanie Dolson added 17 points and nine rebounds. The Mystics scored 34 first-quarter points and 53 first-half points, both season highs.
Abby Bishop had 17 points for Seattle (5-14), which has lost seven straight on the road.
The Mystics led by as many as 24 points in each half. Seattle cut the deficit to 57-45 midway through the third quarter before Washington went on a 12-5 run, capped by a steal and six consecutive points from Latta.
The Mystics Kia Vaughn, who has been out since June 12 with concussion symptoms, had eight points and four rebounds in front of 10,100 on youth camp day at the Verizon Center.