Naomi Osaka was eliminated from the Italian Open on Monday after being beaten by Peyton Stearns 6-4, 3-6, 7-6 (7/4) as her struggles for form at the top level continued.
In the quarterfinals, Stearns will face one of Danielle Collins, who knocked out reigning champion Iga Swiatek, or Elina Svitolina after coming through an attritional match which lasted two hours and 43 minutes on a baking centre court.
Osaka is another big name that American Stearns has beaten in Rome after also knocking out fifth seed Madison Keys in the previous round.
Former world number one Osaka has looked a long way from the player who has won four Grand Slams since returning last year from a 15-month break from tennis for the birth of her daughter.
Her comeback was also hampered by an abdominal injury that forced her out of the Australian Open, after which early exits at Indian Wells and Madrid highlighted how far she was from her best.
Osaka warmed up for Rome by winning a minor event in Saint Malo in France, earlier this month.
But she has failed to get past the last 16 of a tournament higher than the WTA 125 series since losing the Auckland final back in January.
Later, Jannik Sinner continues his bid for a first Rome title against lucky loser Jesper de Jong who will come up against not just the world number one but also a partisan crowd.
No Italian has won the Rome title since Adriano Panatta in 1976, and Monday's match will be seen as another warm-up as Sinner tries to find top form ahead of the French Open which starts later this month.
Sinner's compatriots Matteo Berrettini and Jasmine Paolini are also in action on centre court, before women's top seed Aryna Sabalenka takes on Marta Kostyuk.