Angel McCoughtry and Tiffany Hayes each had 16 points to help the Dream (12-5) win for the ninth time in 11 games and improve to 3-0 against the Mystics this season.
Tied at 40 at the half, the Dream had a 26-12 edge in points in the paint in the second half. They also had 14 of their 18 fast-break points in the second half.
Lyttle credited the Dream's second-half surge to conditioning, saying coach Michael Cooper makes the players, "run so much (in practice) that other teams cannot keep up with us. We run, run, run and when we're tired, we run some more."
Cooper did not feel well after the game, so assistant Karleen Thompson met with reporters and explained the difference between halves. Atlanta, she said, "Just attacked the basket . . . (and did) not settle for jump shots."
Emma Meesseman led Washington (7-12) with 18 points. After shooting 16 for 36 in the first half, the Mystics were 11 for 29 in the second. They were 1 for 6 from 3-point range in the second half and 3 of 12 overall.
"Every day is a struggle for us," Mystics coach Mike Thibault said. "We're last in the league in 3-point shooting (27 percent), and last year we were one of the better shooting teams. We aren't making open shots."
The Mystics missed eight of their final nine shots.
"Right now, it's no one thing," Thibault said. "It's missing a layup, fouling at the other end, missing a block-out on a rebound. All of a sudden it snowballs."
Atlanta pulled away for good with a 10-2 run. Lyttle's fast-break layup with 2:31 left gave the Dream an 80-67 lead.
Atlanta outscored Washington 12-4 in the paint in the third quarter. Rookie guard Shoni Schimmel's off-balance 3-pointer with 2 seconds left in the third made it 66-57.