Harriet Dart is into the second round of the US Open after beating in-form Daria Kasatkina 7-6(8) 1-6 6-3.
It is the world No. 88’s first win against a top 10 player in her career.
"I'm a little bit in shock right now," she told Amazon Prime.
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"Physically I don't feel great but I really tried to stick at it and push through. I can't believe I got the win.
"What's so exciting about women's tennis is anyone can win."
The first set had ten breaks of serve, but Dart saved two set points and was able to battle to a tie-break where she emerged victorious.
Kasatkina responded instantly in the second set, though, winning it in style to set up a decider.
Dart berated herself for being "so unfit" when she was 2-0 down in the third set, but she fought back from 3-1 down to win the match in two hours and 30 minutes.
Dart, who had never won a main draw match at the US Open before Monday, will play Hungary’s Dalma Galfi in the second round.
If Emma Raducanu loses her first round match against Alize Cornet on Tuesday, Dart would be only 11 points short of her total in ranking points and would therefore be just a single win away from becoming British No 1.
Analysing Dart's historic win, Eurosport tennis expert Mats Wilander said: “Harriet Dart is not a player that you’d think has enough power to disturb Kasatkina. Is it a step in the wrong direction [for Kasatkina]?
“Maybe but you feel like Daria is on her way back. Love watching her play tennis. A great win for Harriet Dart but I’m sure we will hear more from Kasatkina for the rest of the year.”
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