Leaks coming from the Capital One Arena roof during halftime delayed the game. Washington's home game against Connecticut on July 28 was postponed and rescheduled because of water leaks from the roof.
Washington (16-10) played its second consecutive game without leading scorer and All-Star Elena Delle Donne (thumb surgery). The Mystics already lost starting guard Tayler Hill (knee surgery) for the season.
In the second game of a four-game homestand, Washington led by 12 after the first quarter and 49-36 at halftime. The dousing continued in the second half. The Mystics have won two in a row.
Candice Dupree scored 26 points for the Fever (9-19). Indiana has lost seven of eight overall and all three games against Washington this season.
Washington entered Saturday 1 1/2 games ahead of the Phoenix Mercury and New York Liberty for fourth place. The top four teams receive a bye into the second round of the league playoffs.
The Mystics won the first meeting with the Fever 88-70 at home on June 11 and took the rematch 72-58 on the road July 14.
Emma Meesseman scored 15 points and Ivory Latta had 13 for Washington.
Erica Wheeler scored 33 points in Tuesday's 81-76 loss at the Liberty but had only eight against the Mystics.
Indiana plays at Minnesota on Friday. The Fever shocked the WNBA leading-Lynx 84-82 on Aug. 4.