Serena Williams crashed out of the Western & Southern Open as Maria Sakkari steamrolled the third seed en route to the quarter-finals.
Sakkari capitalised on a fatiguing Williams to stun the 23-time grand slam champion 5-7 7-6 (7-5) 6-1 at the WTA Premier tournament on Tuesday.
Williams was two points away from serving out the match in the second set, but 13th seed Sakkari rallied from 5-3 and a break down to prevail after two hours, 17 minutes.
Sakkari, having already claimed the scalp of American sensation Coco Gauff, will meet Johanna Konta for a spot in the semi-finals.
With the US Open on the horizon, Williams – who was two points from defeat in her opening-round match – raced ahead 5-2 against Sakkari in New York, where the event is being held instead of Cincinnati amid the coronavirus pandemic.
Sakkari managed to level the set at 5-5 before former world number one Williams, who voiced her displeasure over a time-violation warning in the ninth game, swept the final two games to clinch the opening set.
Not overawed, Sakkari started the second set by breaking two-time Cincinnati champion Williams as she earned a 3-1 lead before the American superstar reeled off the next four games to set up the opportunity to serve for the match.
But Sakkari thwarted Williams, earning a break point to level the set once more before eventually prevailing in a tense tie-break, having found herself down 4-1.
It was one-way traffic after Sakkari levelled the match – the Greek surging 5-0 ahead of Williams, who managed to avoid a bagel in the final set.