Defending champion Naomi Osaka was knocked out of the US Open by Switzerland's Belinda Bencic, who secured a quarter-final spot against Donna Vekic. Bencic won in straight sets, 7-5, 6-4 – her third win against the same opponent so far this year. Osaka double-faulted on game point in the first game of the match, and she had to gather herself to save four break points in the third game to stay in touch with the Swiss. The world number one then won three games in a row to get it back on serve, but Bencic always threatened, and broke Osaka once more before serving out to take the first set 7-5 – a set in which she hit no aces to Osaka's six, and four double-faults to Osaka's two. But Osaka's errors were key – serving another double-fault in the fifth game of the second set to give Bencic another break, which proved to be decisive. It was at that point the defending champion called for a trainer to come to court, perhaps troubled by an ongoing left knee problem. The 13th seed did not allow her momentum to be interrupted, though, and served to love to finish the match in style, reaching her first Grand Slam quarter-final since 2014. "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."