By Mike Dickson for the Daily Mail
Published: 19:38 BST, 9 September 2020 | Updated: 20:16 BST, 9 September 2020
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 let to a 6-4 win
She was left awaiting the winner of the night match Victoria Azarenka and Elise Mertens, and will play 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