World number two Aryna Sabalenka cruised past American Shelby Rogers despite battling with what appeared to be a groin injury.
The Australian Open champion won the American 6-4 6-3 on Friday night to set up a tie with Czech Marie Bouzkova.
She started well in the opening set and took charge of proceedings but had to call a medical timeout in the first game of the second set as she struggled with her left thigh.
The injury hampered her movement and Rogers had break points for a 3-0 lead before the Indian Wells runner-up regained her footing to dominate the remainder of the match from 3-1 down and win the final five games at the Hard Rock Stadium on Friday night.
"For now I feel fine," said Sabalenka, who is the highest-ranked player in the draw after defending champion Swiatek withdrew ahead of the tournament with a rib injury.
"I will try to fix this problem and be ready for the next match.
"It was definitely a tough match. Super happy that even if I was struggling with my leg a little bit I was able to finish the match in two sets."
The result means that the Belarusian improves to 18-2 on the season and 4-0 lifetime against Rogers.