Washington Mystics coach Mike Thibault had a simple formula for muting the Las Vegas Aces' high-scoring offense Tuesday night.

"Run like hell getting back," Thibault said.

Washington followed his advice, allowing no fast-break points and limiting Las Vegas to 40.6 percent field goal shooting in an 83-73 win that polished off a 3-0 season series sweep.

Now the Mystics (20-12) face an even bigger challenge Friday night on the road against the Chicago Sky (23-8): Keep the league's best team in check after it sustained an unexpected home loss Tuesday night to Dallas.

Chicago could have opened up a two-game lead on the Aces for the No. 1 seed in the WNBA playoffs, but instead fell 84-78 to a Wings team scrapping to earn a playoff spot. The Sky were just sloppy enough (16 turnovers) and missed eight free throws, which led them to lose against an opponent that went 21-of-25 at the line and stole the ball a dozen times.

Wasted in the defeat was another good game by leading scorer Kahleah Copper, who finished with 19 points and 11 rebounds. It wasn't enough to beat a short-handed Dallas team that was missing leading scorer Arike Ogunbowale due to injury.

Veteran point guard Courtney Vandersloot said the team isn't concerned with playoff seeding.

"We're focused on us, making sure we're getting better," Vandersloot said. "We have a lot of things to improve on."

As for Washington, it's tied with Seattle for the fourth seed if the playoffs started now instead of on Aug. 17. The Mystics lost the season series to the Storm, though, so they'll have to finish a game ahead in the standings if they want home-court advantage for the first round.

Washington looked like a championship contender Tuesday night, getting 16 points and nine assists from Natasha Cloud while controlling the boards 38-30. The Mystics allowed just three offensive boards.

This is the final game of the season series, with the Sky leading 2-1. Chicago and Washington split a two-game home-and-home series in June, each team winning at home.