US Open: Venus is defeated by Zheng Jie

Williams has only reached the third round at a grand slam once in the past two years, losing more than her fair share of close matches.

And this was another one, Zheng eventually coming through 6-3 2-6 7-6 (7/5) and then apologising to the crowd for beating one of their favourites.

Rain made the final stages even more dramatic, with Williams breaking Zheng when she served for the match and forcing a tie-break, and she really should have brought up the first match point.

But at 5-5 she dumped a simple volley in the net and then put a backhand wide to hand victory to her opponent after three hours and two minutes.

Williams said: "I should have made the shot. I think I was just rushing. I rushed so badly.

"I had a lot of opportunities in the match. I was always stepping up and putting myself in a good position. So this is a great sign. I'm just not playing consistently enough.

"I just dug myself into so many holes the whole match. I just fought as hard as I could to get out of them, but sometimes it wasn't enough."

There is rarely a Williams press conference these days where she is not asked about retirement, but she has never given so much as a hint that she is thinking about it.

Asked whether she sees herself playing singles again at the US Open, she said: "I definitely want to come back for the atmosphere.

"Next year's Open is so far away right now. I have to think about the doubles, think about this fall, playing maybe quite a few tournaments until the season is over just to get some momentum going into next season."