Connecticut (21-9) is a game behind first-place Washington. The top two seeds get a bye to the semifinals, and the third and fourth seeds receive a bye to the second round. Seattle (15-15) has clinched a spot in the playoffs for a chance to repeat as champion.
Jonquel Jones added 10 points for Connecticut, which is 7-8 on the road this season. Thomas scored 20-plus points for the sixth time this season, moving within 17 points of reaching 2,000 for her career. Shekinna Stricklen sank a 3-pointer to move into a tie with Penny Taylor for 20th on the WNBA 3-pointers made list.
Connecticut shot 53% and outrebounded Seattle 43-30 to sweep the season series.