Osaka, 27, gave birth to daughter Shai in July 2023 and returned to the WTA Tour six months later.
The four-time major winner lost in the first round on her Slam return at the Australian Open last year, before exiting in the second round at Roland Garros, Wimbledon and Flushing Meadows.
But the former world number one is off to an impressive start in 2025, beating France’s Caroline Garcia in three sets in her opening match before overcoming 20th seed Muchova in just under two hours.
“Honestly, it took everything,” Osaka said of her comeback victory on Wednesday.
“I felt like I left everything I had on the court. Just to be back on these courts… it really makes my whole year.”
Osaka will play Belinda Bencic in the next round, with the Swiss herself playing her first Grand Slam since giving birth to daughter Bella in April 2024.
A third straight victory would send Osaka into the fourth round at a major for the first time since she won the Australian Open in 2021.
