Initially there was real concern for Nadal but he recovered quickly and was keen to play down the incident as a normal occurrence after a match contested in hot and humid conditions.

After her three-hour win over Svetlana Kuznetsova last night, Wozniacki, with a big grin on her face, imitated the defending champion by sliding down her chair.

She wrote on Twitter today: "Had a bit of fun last night b4 my press conference.Hope it was not taken the wrong way. I have the upmost respect and admiration of Rafa!!!!"

Wozniacki is no stranger to antics in the press room. At the Australian Open this year, after hearing reports that journalists considered her boring to interview, she spent one press conference pre-empting questions and offering stock answers before inviting journalists to ask her "questions that are a little more interesting".

That led to her being quizzed on Kenny Dalglish's appointment as Liverpool manager and how to solve global warming, while on another occasion she made up a story about being attacked by a kangaroo before later confessing she had been lying.

At Wimbledon she turned from interviewee to interviewer in Novak Djokovic's pre-tournament press conference, asking the Serb a series of questions.

Wozniacki was left to reflect on a very satisfying evening which should give her tremendous belief for what is a very tricky road ahead.

The Dane said: "It definitely gives you confidence to pull this match out. I felt like I played some good tennis out there. We had some unbelievable rallies at some points. I was moving very well.

"I think I handled the wind pretty well as well, so I'm just happy to be through to the quarter-finals. I could have been sitting here and been out already. But I'm very proud of what I've achieved today."

For Kuznetsova, who made 78 unforced errors, there was a sense of deja vu after she also lost a tight match to eventual finalist Wozniacki at Flushing Meadows two years ago in the fourth round.

The Russian felt she paid for missing her chances, and she said: "I have not played a match so intense in a very, very long time. My US series wasn't so good. Finally I came here in good shape and was playing a good game.

"Yes, I did lots of unforced errors, but because I was trying to play very aggressive and to dictate, and I was doing this. She was a wall. To break a wall, you cannot hit hard. You have to mix it up.

"I think I did the right things. I just couldn't close it up in the right moments. This is it. She never gives the match away. I just didn't do the right things in certain moments when I had to."