Danielle Adams totaled 12 of her 19 points in the second half, as San Antonio survived its first test without Becky Hammon, topping Phoenix by an 88-80 count on Wednesday.
Hammon was diagnosed with a season-ending ACL tear on Monday.
DeLisha Milton-Jones added 16 points, while Shenise Johnson, Jayne Appel and Danielle Robinson each had 13 for the Silver Stars, who snapped a three-game losing streak.
Candice Dupree scored 22 points and Diane Taurasi had 20 before fouling out late in regulation for the Mercury, who have lost two straight after winning five in a row.
Brittney Griner was out of action for the hosts, thanks to a sprained left knee.