Japan’s top-ranked player reeled off eight consecutive games at one stage to power into the quarter-finals.
It had all seemed to be going to plan for the American second seed Williams when she broke the 19-year-old Osaka in the fifth game of the opening set.
But then the Williams first serve deserted her when serving for the set at 5-4.
Today I accomplished one of my dreams ❤️❤️❤️
— NaomiOsaka大坂なおみ (@Naomi_Osaka_) October 11, 2017
Two double faults and a series of fierce ground strokes from Osaka which unerringly kissed the lines enabled the world number 64 to break twice and take the set 7-5.
“She played well,” a disappointed 37-year-old Williams told reporters. “You know I made a few errors at 5-4 and after that she played pretty flawless. I can only give her credit.”
Osaka, who had made headlines when she knocked Angelique Kerber out of the US Open in the first round last month, continued in the same vein at the start of the second set and raced into a 5-0 lead.
“I felt like I played offensively and hit really deep hard balls but she had the luck today and could return those balls even harder and deeper,” said Williams.
Williams briefly rallied to 5-2, but after a pep talk from Osaka’s coach, the Japanese refocused and closed out the match on her serve at the second time of asking after an hour and 24 minutes.
“Venus is someone I’ve respected and admired,” said Osaka, who had not been born when Williams reached her first Grand Slam final, at the 1997 US Open.
“I’ve grown up watching her. Even though she someone I admire, it’s just another opponent at the end of the day so I tried to focus hard.
Teenager topples No.2 seed Williams 7-5, 6-2! pic.twitter.com/TPfb3ZTAbX
— WTA (@WTA) October 11, 2017
“I feel like even if I hit one semi-short ball she would come in and crush it, so I had to play really well.”
Earlier, the seventh seed Daria Gavrilova battled into the quarter-finals with a 6-1, 2-6, 6-2 win over American Shelby Rogers.
Rogers and Gavrilova renewed their rivalry at Victoria Park after last month setting a record for the longest ever women’s singles match at the US Open with a three hours and 33 minute epic.
“I was really motivated,” said the world number 22 Gavrilova after avenging her Flushing Meadows defeat.
“She has such a great serve I knew I had to take my chances on her second serve.”
Rogers had come out on top 7-6, 4-6, 7-6 in their marathon New York encounter but on this occasion Gavrilova raced to win the first set 6-1 in just 26 minutes.
Rogers, ranked 55, hit back immediately to take the second 6-2 in a scrappy encounter littered with errors.
With both players coming under pressure on their serve in the final set it seemed a matter of who would crack first.
And at 2-2 and 0-30 it was Rogers who blinked, serving back-to-back double faults to hand the Russian-born Australian the crucial break.
Another followed and the Australian closed out the match in an hour and 44 minutes.
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