Caroline Wozniacki showed she is back as a force in women's tennis by stunning Maria Sharapova to reach the quarter-finals of the US Open.
The hugely popular Dane produced a display of real quality to win 6-4 2-6 6-2 and make the last eight at a grand slam for the first time since the Australian Open in 2012.
The last time the Dane beat the Russian was at Flushing Meadows at the same stage four years ago, when she was in her pomp.
Wozniacki has been in fine form and was the better player in the opening set, but it was no surprise to see Sharapova hit back in the second.
Because of the hot and sticky conditions, the heat rule was in effect, meaning a 10-minute break between the second and third sets.
Sharapova took too long, though, and was given a time violation, while Wozniacki then complained to the umpire about the time her opponent was taking between serves.
Wozniacki came out for the decider with a real sense of determination and purpose and made the breakthrough in spectacular fashion in the fourth game.
Somehow the 10th seed chased down a succession of lost causes before Sharapova netted a volley, prompting Wozniacki to whip up the adoring crowd.
And there was no wavering from the 24-year-old, who seized her first opportunity to clinch the match with a backhand winner that cleaned the line.
Wozniacki said: "It means so much to me. Things have been a bit up and down this year. To win against a champion like Maria is an unbelievable feeling."
In the quarter-finals, Wozniacki will play 13th seed Sara Errani, who ended the emotional run of qualifier Mirjana Lucic-Baroni.
The Croatian was back in the fourth round at a slam for the first time since reaching the Wimbledon semi-finals aged 17 in 1999.
Family and financial problems derailed her career but her love for tennis never wavered and she is finally back on the big stage.
The statistics told the story of a match between two very different players, with Lucic-Baroni hitting 46 winners compared to just four for Errani.
But ultimately the Italian's tally of nine unforced errors and Lucic-Baroni's mark of 69 proved the difference in Errani's 6-3 2-6 6-0 victory.
Lucic-Baroni described her upset of second seed Simona Halep in round three as the best day of her life, and she said: "This has been a great two weeks, the best I can remember for a long time.
"Obviously right now I'm really disappointed. She's a really tough player to play. Today I felt like I ran out of gas a little bit. It's tough to win against her that way.
"I knew I was going for too much. It was really difficult to play because it was very windy day. It was really difficult to time the balls, especially on her ball and her serve. It comes so slow and it kind of floats in the air."
Lucic-Baroni will return to the top 100 thanks to her six victories here and is projected to achieve her highest ranking since 2000 when the standings are updated.
"I'm very motivated to have a great off-season, to work the hardest I have ever worked, and have another great year next year," she said.
Errani has averaged less then 80mph on her first serve throughout the tournament but her accuracy with it is almost 90 per cent.
The 27-year-old said: "Of course I have to improve it a lot, but it's not easy. I try. With that serve I have been five in the world, so it's not that bad I think.
"It's a bit different to the others. I don't try to hit the strongest I can. Maybe I can sometimes try to push more, but I don't want that. I want consistency. I need to start the point where I want."
Belinda Bencic became the youngest quarter-finalist at the US Open since her Swiss compatriot Martina Hingis won the title in 1997 with a 7-6 (8/6) 6-3 victory over ninth seed Jelena Jankovic.
The 17-year-old works with Hingis' mother and former coach Melanie Molitor and the two are very close.
It was Bencic's second victory over a top-10 player in a row after her third-round win against Angelique Kerber.
Speaking after that match, Hingis said of Bencic: "I think there is huge potential for her.
"I definitely think she can be top-five. She's on the way to get there. How far, it's up to her. Nobody can play the matches for her and win matches, win the tournaments.
"But she showed that she can win a big match when she has to. Hopefully there will be more opportunities in the near future. Maybe here."
Jankovic was the highest-ranked player left in the bottom half of the draw and that status now belongs to 10th seed Wozniacki.
In the last eight, Bencic will meet another unseeded player in China's Peng Shuai, who reached her first slam quarter-final by beating 14th seed Lucie Safarova 6-3 6-4.