By Piers Newbery
BBC Sport at Flushing Meadows
Britain's Jo Konta stunned ninth seed and Wimbledon finalist Garbine Muguruza in an epic contest at the US Open.
Konta, ranked 97th, won 7-6 (7-4) 6-7 (4-7) 6-2 after three hours and 23 minutes - a record for a women's match in New York.
The 24-year-old has now won 15 matches in a row and is into the last 32 of a Grand Slam for the first time.
She will face German 18th seed Andrea Petkovic in the third round on Saturday.
"To be honest, I'm so tired - I think both of us are," said Konta, who has guaranteed herself the biggest pay cheque of her career of at least $120,200 (£78,900).
"I didn't think she probably played her best today but credit to her, she's an incredible fighter and no matter what level she brings, she always brings her top-10 mentality.
"I had to fight for every point, it wasn't given to me, and I'm just happy to come back another day."
It is Konta's second win over a top-10 player, the first coming against world number eight Ekaterina Makarova at Eastbourne in July.
New York record breaker
American Madison Brengle and China's Saisai Zheng had set a new mark on Monday at three hours and 20 minutes, but it lasted just three days.
Konta's final service game took her match to a new women's singles record for Flushing Meadows.
It is the longest women's match at the US Open since the tie-break was introduced in 1970.
"I was just fighting for each point, running down each ball and trying not to sit down at the end of the court after each point," said Konta.
Konta keeps her cool
The Briton converted a remarkable run of form over the North American hard-court season into the biggest win of her career on the Grand Slam stage.
It was Konta who made the running for the most part on a scorchingly hot court 17 at Flushing Meadows.
She took her seventh break point to move 4-3 ahead and recovered her poise to edge a tense tie-break after failing to serve out at 5-4.
Muguruza, 21, pushed hard in the second but Konta stood firm, coming back from 0-40 in a 12-minute game at 1-1 and later breaking back when the Spaniard served for the set.
It took a contentious call at 3-5 down in the tie-break to finally rattle the Briton - although it appeared the correct decision - and Muguruza went on to capitalise on her second set point.
The players briefly escaped the stifling conditions before the final set and it allowed Konta to cool down both mentally and physically.
An increasingly frustrated Muguruza was vulnerable on her forehand and second serve, and Konta rediscovered her earlier poise, breaking twice to lead 4-0 and serving out in style.
What's changed for Konta?
Since that breakthrough run to the quarter-finals at Eastbourne, Konta has lost just one match - against Russian Maria Sharapova in the first round of Wimbledon.
She then collected back-to-back titles on the lower-level challenger tour in Canada, won three matches in US Open qualifying and has now beaten American Louisa Chirico and Muguruza in the main draw.
Konta is well on course to challenge Heather Watson, ranked 61st, for the position of British number one.
•Konta relocated her training to Gijon in northern Spain at the end of last year under the guidance of coaches Esteban Carril and Jose-Manuel Garcia.
•She has also been working with "mental coach" Juan Coto, a London-based Spaniard who also works with hedge fund managers and city workers.