Serena Williams, No.3 seed, remains on course for a 24th Grand Slam title after overcoming No.15 seed Maria Sakkari in three tough sets 6-3, 6-7(6), 6-3.
Overcoming Sakkari would be no easy task, as she was seeking to become the first Greek player to make a Grand Slam quarterfinal.
The pair had met two weeks previously in the last 16 of the Western and Southern Open, when Williams let a set and break lead slip to lose.
Williams had initially looked vulnerable when she went a set down, it was Sakkari who had the faster start.
It was experience and determination that ultimately told has momentum changed.
At 3-3, 30-30, Serena sent down a thumping serve that equaled her fastest of the tournament, and she used that as a foundation not only to finish off the game, but also to break her opponent.
The victory was sealed at the second time of asking, an expressive cry, testimony to how close Sakkari had been to halting her dream.
Williams’ next opponent is Bulgaria’s Tsvetana Pironkova, who has never reached the US Open quarter-finals before and is playing her first tournament since Wimbledon 2017.