The 21-year-old won five games in a row to win the opening set in her first match since losing in the Wimbledon last-16 earlier this month. However, Mertens, the eighth-seeded Belgian, came back strong to win the second set.
Raducanu was contending with a five-hour time difference as the last set continued until 11 p.m., having landed on the east coast of the United States from the United Kingdom on Thursday.
However, the former US Open winner overcame Mertens for the second time this month after winning the first set by demonstrating her mental toughness and saving five break points at one point.
Raducanu stated, “I was playing some fairly nice tennis throughout, especially in the first set and a few spots in the third set.
“In the second, my concentration wavered. It’s challenging to play at 11:30. I arrived on Thursday night, so my jet lag is still there.
Raducanu declined the chance to compete in the 2024 Olympics because she did not want to return to playing on clay prior to the hard court season. She is still recovering from surgery on her ankle and wrist.
