She was quickly down two more breaks at 4-0 before squandering three break points in the sixth game as Osaka glided into a maiden semi-final at the Slams.
Madison Keys of the US celebrates match point against Carla Suarez Navarro of Spain in a quarterfinal match on day ten of the 2018 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center.
Keys made it all the way through to the final a year ago before she was stopped by fellow American Sloane Stephens at Flushing Meadows.
Williams stayed on the charge and Sevastova's morale sagged as she was broken twice in the second set, her elegant backhand letting her down and it was one-way traffic from there onwards with Williams winning twelve of the last thirteen games.
"Great! I want to see her go against Serena in the final", said one Twitter user. She recovered to win in three sets, with her opponent accusing her after the match of acting.
She leads Osaka 3-0 in head to head and most recently defeated the 20th seed in straight sets in the third round at Roland Garros in June. At her second major back, Wimbledon, she was the runner-up.
He played back-to-back four-setters against Karen Khachanov and Nikoloz Basilashvili before recovering from breaks down in the third and fourth sets against Thiem.
It was another hot afternoon Wednesday, with temperatures in the high 80s but feeling about 10 degrees hotter with the humidity.
"It means a lot", she said.
Tsurenko didn't appear bothered by the conditions, but whether it was her health or just first-time jitters, she was off from the minute she stepped onto Arthur Ashe Stadium.
On Wednesday, Osaka only needed 12 winners because a whopping 31 of her other points came via unforced errors by Tsurenko. "I used to play here when I was a little kid, so these courts aren't new to me", Osaka said. "I wasn't nervous before the match, but as soon as I got into the court, it was different". "I still haven't totally processed this match".
Next up for Nishikori is a clash against either two-time champion and former world number one Novak Djokovic or John Millman, the Australian who stunned Roger Federer in the fourth round. He made the best possible start on another scorching hot day in NY by racing through the opening set in 36 minutes.