Tiffany Hayes had 19 points and Aneika Henry added 15 points and 12 rebounds to help Atlanta (18-14) snap a five-game losing streak. The Dream, who averaged 71.4 points during their skid, were without leading-scorer Angel McCoughtry for the second straight game due to tendinitis in her feet.
Erin Phillips scored 21 points to lead the Mercury (27-5), who have already secured the top spot in the West and home-court advantage throughout the WNBA playoffs. Shay Murphy had 11 points and Tiffany Bias added 10.
Most Valuable Player contender Diana Taurasi and starting guard Penny Taylor were healthy scratches for the Mercury, who won 21 of their previous 22 games.
Phoenix was held to 42.5 percent shooting and trailed by as many as 28 points in the second half.
Mercury All-Star center Brittney Griner finished with nine points, five rebounds and three blocks. She increased her single-season blocks record to 125 before sitting out the final 14 minutes of the game, which was never closer than 12 points in the fourth quarter.
Atlanta took control in the second quarter when it scored a season-high 37 points, led by 20 from Schimmel. The Dream turned an eight-point first-quarter deficit into a 55-41 halftime lead by connecting on 15 of 18 free throws in the quarter.
Schimmel, who was named the All-Star game MVP after scoring 29 points, eclipsed her previous season-high in scoring in less than 11 minutes during the first half.
The Dream and Mercury split the season series 1-1.