needed a medical time out in the second set of her 6-3 6-4 win over Petra Martic on Sunday to get treatment on her right ankle but recovered to advance to the US Open quarter-finals.
Williams fell to the court at 2-2 in the second set after charging to the net to hit a volley that sailed long.
The 37-year-old American eighth seed got treatment on her ankle during the changeover and appeared to be fine, smacking 38 winners on a sunny day at Arthur Ashe Stadium court.
Williams blasted her fourth ace on match point to see off 28-year-old Croatian Martic and reach the last eight, where she will face Wang Qiang of China for the first time.
Serena Williams advances in New York despite ankle injury