The first set was dominated by the world No. 13, but Cirstea hung tough in the second and pinched it in the tiebreak. After that, Cirstea never looked back.
Djokovic immediately rushed over to check if she was okay and placed his hand on her back as the judge struggled for air. After a few minutes she was able to get up and walked off the court.
The bumpy restart might have convinced Loew that he can't entirely rely on his backups like Julian Draxler (Paris) and Julian Brandt (Dortmund). His full-back problem hasn't been solved after picking Robin Gosens (Bergamo) and Thilo Kehrer (Paris).
Rodriguinho had given Bahia the lead at Internacional's Beira-Rio stadium when he cut onto his left foot and slotted a low shot into the bottom left corner.
"It's a great result for Wolf because in my first four majors I only won one match," Medvedev said. "In his first one he has already won two, so I'm sure he's going to be climbing up the rankings and playing good."
Team captain Sergio Ramos continues to be vital, as much for his ability to intimidate rivals as for his positional sense, and the 34-year-old is showing few signs of slowing down, while Zidane will be looking for more progress from young Brazilian wingers Vinicius Jr and Rodrygo.
The result at Morumbi stadium marked Sao Paulo's fourth victory in five matches and lifted the Tricolor to second, a point behind Internacional.
She will take on 15th-seeded Maria Sakkari of Greece in the last 16, who stunned Williams at last month's Western & Southern Open.
Since the start of the summer transfer window, the London club have added the German duo Werner and Havertz, Morocco's Hakim Ziyech, England's Ben Chilwell and Brazilian veteran Thiago Silva to their squad. Enditem
"Ensuring a safe return to international table tennis has been our utmost priority ever since the pandemic broke out. We have managed to get events back up and running before the end of 2020," ITTF president Thomas Weikert said. Enditem
Djokovic's exit means there will be a first-time Grand Slam champion in the men's draw, with Zverev among the contenders at Flushing Meadows.