Wozniacki said: “It means a lot to me. The season for me has been a little bit up and down, and it’s so nice to start feeling like I’m playing the way I want to.

“I have had a great summer. I told Serena I’m pretty tired of her. Twice she beat me in three sets. I said, ’Can you just get out of my way’? We laugh about it.

“This one was a great win for me. Maria is a good player. For me, I think mentally to get that in my pocket is nice. I still have hopefully a few good matches in me here in this tournament. It’s just exciting to be in the quarters once more.”

The last time Wozniacki beat Sharapova was at Flushing Meadows at the same stage four years ago.

The Dane looked confident from the start 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 has had to watch Rory McIlroy win two majors since their high-profile split earlier this summer and such a difficult time in her life has surely played a part in her revival.

Wozniacki is keeping her cards close to her chest on that subject, though, saying: “I’m here to play tennis and I play well. I’m just happy to be here. Whatever is happening off the court is not really relevant here.”

Sharapova won her fifth grand slam title at the French Open but has failed to go beyond the fourth round at any of the other slams this year.

She praised Wozniacki, saying: “I thought she played really well. She made me hit a lot of balls. That’s always been her strength. But she did extremely well today. She’s a great retriever, especially in these types of conditions. I just felt like I maybe went for a little too much.”

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 in the big time.

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.”

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.