By Rory Carroll
NEW YORK (Reuters) - Holder Naomi Osaka of Japan was upset 7-5 6-4 by Belinda Bencic in the fourth round at the U.S. Open on Monday as the Swiss reached the quarter-finals for the second time.
Bencic, seeded 13th, broke the world number one in the first game of the match under the closed roof of Arthur Ashe Stadium and her superior serving carried the day as she won 82% of her first serve points on a rainy day in New York.
Momentum swung firmly in the 22-year-old Bencic's direction in the second set when Osaka double faulted to hand the Swiss a 3-2 lead and the top-seeded Japanese, who appeared to struggle with a troublesome left knee, was unable to recover.
The win meant Bencic improved to 3-0 this year against the 21-year-old Osaka, who came through an emotional straight sets win over 15-year-old American Coco Gauff in the third round.
Bencic, who also reached the quarter-finals in 2014 but has struggled with injuries in recent years, said that taking Osaka's powerful serve early was key to her victory.
"I was so excited to come on the court, the challenge could not be bigger so I had to be on top of my game," she said in an on-court interview.
"I'm really pleased with how I played and how I managed my nerves in the end," she added.
"I'm not the person with the most winners or aces, I had to play it a bit like chess with tactics on the court."
Next up for Bencic is a meeting with Donna Vekic, who came from behind to see off Julia Gorges with a 6-7(5) 7-5 6-3 victory on Louis Armstrong Stadium court.
(Reporting by Rory Carroll; Editing by Ken Ferris and Christian Radnedge)