The Sky (15-17) improved to 5-1 since Delle Donne returned from a flare-up of Lyme disease, including two victories over the Mystics. The win pulled Chicago into a second place tie in the Eastern Conference with Washington.
The Mystics (15-17) have lost four of six games. Like Chicago, Washington could reach the postseason by winning one of its final two games.
''It has been interesting in the East and thankfully so,'' Sky coach Pokey Chatman said. ''We've been through a lot, but we're still right there.''
Delle Donne and Fowles have missed a combined 30 games this season. But they weren't missing shots on Wednesday, finishing a combined 14 for 20 from the field.
Despite not having those All-Stars for chunks of the season, Chicago can make the playoffs by winning one of its last two games. The Sky have been playing with a postseason mentality for the past several games.
''That's great preparation for the playoffs,'' said Delle Donne, who made 7 of 9 shots off the bench. ''We kind of like that, kind of like the tension.''
Monique Currie scored 18 points and rookie Stefanie Dolson had 12 points and 10 rebounds in her first career start. Washington played without leading rebounder Kia Vaughn (suspension) and guard Kara Lawson (sprained ankle).
With 6-foot-6 Fowles inside, Chicago outrebounded the shorthanded Mystics 41-29 and finished with a 42-30 scoring advantage in the paint.
''She's pretty big. She's an amazing player,'' Dolson said of Fowles. ''Not having Kia for this one was pretty big.''
Washington offset its 35-percent shooting from the field by making 16 of 19 free throws. Chicago made all six of its attempts in the final 44 seconds.
Down 11 points in the first half, Washington trailed 70-69 with 8.9 seconds remaining following Bria Hartley's layup on an intercepted inbounds pass. Epiphanny Prince's two free throws put Chicago up 72-69 with 7.8 seconds left. Washington's potential game-tying 3-pointer missed badly.
Chicago plays at Indiana on Saturday and hosts San Antonio on Sunday.
Washington's next game is Friday at Connecticut. Vaughn was suspended for throwing an elbow in the Mystics' double-overtime road loss at the Sun on Sunday.
''It doesn't have to be pretty. It doesn't have to be great. We just need a win,'' Currie said. ''We're going to do whatever we can - except throw elbows. We don't want to have anybody suspended again.''