Williams withdrew with a left knee injury, tournament officials said. It is the second consecutive WTA event in which the American has been unable to continue, after her retirement from last week's tournament in Indian Wells with a viral illness.
Serena Williams made another sudden tournament exit, this time blaming a previously undisclosed left knee injury.
Williams withdrew Saturday from the Miami Open, an unexpected move because she showed no signs of injury while winning her opening match a day earlier against Rebecca Peterson, 6-3, 1-6, 6-1.
Williams didn't mention any problems with the knee during a news conference after the match, and the WTA had no information regarding when she was hurt. She wasn't scheduled to play Saturday.
Her stay at the tournament was also brief last year when she lost.
Friday's match was Williams' first since she retired at Indian Wells two weeks ago because of a viral illness.
Williams, 37, has played only eight matches this year. She hasn't won a tournament since the 2017 Australian Open, before she took a break of more than a year to become a mom.
The victory Friday was Williams' first in Hard Rock Stadium, the Miami Dolphins' home and the tournament's new centre court. The Miami Open moved this year from Key Biscayne, where Williams won eight titles.
She was next scheduled to play No18-seeded Qiang Wang, who advances to the fourth round.
"I am disappointed to withdraw," Williams said in a statement. "It was an amazing experience to play at Hard Rock Stadium this year, and I would like to thank the Miami Open for putting on an amazing event. I hope to be back next year to play at this one-of-a-kind tournament in front of the incredible fans here in Miami."
Williams happens to own a small share of the Dolphins, and she took part in this week's ribbon-cutting ceremony.