New York (AFP) - Reigning champion Naomi Osaka was knocked out of the US Open by Swiss 13th seed Belinda Bencic 7-5, 6-4 in the last 16 at Flushing Meadows on Monday.
Bencic defeated Osaka for the third time in as many meetings this year and will play Croatian 23rd seed Donna Vekic in the quarter-finals. Osaka will lose the number one ranking to Ashleigh Barty as a result of the loss.
"The challenge cannot be bigger against Naomi. I had to be at the top of my game and I'm really pleased how well I handled my nerves at the end," said Bencic, who also beat Osaka at Indian Wells and Madrid.
"I'm trying to play like chess and make it tactical on the court," she added. "Taking the serve early, trying to anticipate because she has so much power."
Bencic, 22, equaled her best at a Grand Slam having reached the last eight on her US Open debut in 2014.
Osaka's exit means there will be four different women's Grand Slam winners in a season for the third consecutive year, a first in the Open era.