Serena Williams reaches US Open semi-final with victory over Tsvetana Pironkova in three sets 

Serena Williams is through to the last four of the US Open, but if she has to dig any deeper she might find herself halfway to Australia.

For the third successive match she needed to recover from a set down, this time against the sorcery of the event’s most unlikely quarter finalist, Tsvetana Pironkova.

Courtside microphones in the ghostly Arthur Ashe Stadium could pick up her frantic breathing between points before she came through 4-6, 6-3, 6-2 in two hours and 12 minutes. 

Serena Williams reached US Open semi-final with a 4-6, 6-3, 6-2 win over Tsvetana Pironkova

The Bulgarian went a set up in the last-eight tie after errors from Williams led to a 6-4 win

She was left awaiting the winner of the night match between Victoria Azarenka and Elise Mertens, and will play her semi-final while enjoying the benefit of a longer rest than her opponent.

Williams may need every minute of it, after taking an hour to work out the wonderfully expansive game of the unranked Bulgarian, one of the three parents in the last eight stage of the women’s singles.

The American proved to be Mother Superior, but could only admire the resourcesfulness of unranked Pironkova, playing her first tournament in more than three years.

‘It just showed me how tough mums are, if you can birth a baby you can do anything,’ said Williams.

‘You play, you go home, and you are still changing diapers. She played unbelievable, I could barely win a match when I came back.

‘I was feeling it a bit in my legs. At the beginning I felt a bit fatigued. I never give up but I need to find out how to start faster.’ 

Williams struggled to get a grip on her opponent and went a set down at Flushing Meadows

The American was broken in the first game of the second but fought back to level the match

It might help if, unlike Wednesday night, she was ready for the time of the match.

Pironkova was forced to wait for ten minutes in the tunnel at the start while, Williams later explained, she had tape on her ankle adjusted because it had been wound too tight.

Two matches stand between her and a 24th Grand Slam title, which would be the first since she gave birth in 2017.

Only her serve and will to win kept her in it, and she was fortunate that the Bulgarian – whose game features a squash-style sliced forehand and deadly backhand – abruptly dropped her level in the seventh game of the second set.

Williams claimed the break point with a 25-shot rally, the longest of the match. She then served it out with three aces, the sound of her heaving chest easily audible in the deserted arena.

You keep expecting these matches to catch up with her at the age of nearly 39 but her mind is the strongest weapon of all. The Bulgarian was spent towards the end, and will now travel back to Bulgaria to see her two year-old son.