Serena Williams moved to within two matches of winning a record-equalling 22nd Grand Slam title with a 5-7, 6-4, 6-1 win over Kazakhstan's Yulia Putintseva in the French Open quarter-finals on Thursday.
But it was a peculiar performance from the 34-year-old top seed and defending champion, who looked unrecognisable for the first hour of a match played in cold, damp conditions on the Roland Garros centre court.
Defeat was staring the out-of-sorts American in the face at a set and a break down, but in the nick of time the champion managed to rekindle the fires that fuel her game.
Back-to-back service breaks allowed her to turn the match on its head and avoid what would have been one of the biggest upsets in French Open history.
Because of the poor weather conditions that have beset Roland Garros this week, Williams will play her third match in three days in Friday's semis against unseeded Dutchwoman Kiki Bertens, who upset eighth seed Timea Bacsinszky of Switzerland.
A win there would qualify her for Saturday's final and the chance of matching Steffi Graf's modern-era record of 22 Grand Slam titles set in Paris in 1999.
"She played unbelievable and I did not think I was going to win that in the second set, but somehow I did," Williams said.
The match got off to a hesitant start with the players coming off during the third game as light rain started to fall.
They were back again on a sparsely-filled Court Philippe Chatrier 10 minutes later and there were looks of surprise as Putintseva, playing in her first Grand Slam quarter-final, broke serve and then held her own to love to lead 3-1.
Williams though quickly pulled out of her lethargic start to break and level at 3-3.
The 34-year-old American, bidding to become the oldest ever female champion at Roland Garros, tried to apply more pressure on her 21-year-old opponent, but there were too many unforced errors in her game.
She paid the price for a sloppy 11th game with Putintseva grabbing the chance to pull off a second break and then serving out to love for the set.
Things went from bad to worse for Williams as she dropped serve to love to start the second set, spraying her shots long and wide.
Her case was starting to look forlorn, but some semblance of normality started to return to her game and back-to-back breaks hauled her 4-1 ahead.
Another scrappy service game from the American allowed Putintseva to pull back level at 4-4 and the defending champion had to stave off two break points in the next game.
That boosted Williams and she profited from a double fault from her Russian-born opponent to take the second set 6-4 minutes later.
The top seed finally got her nose in front with a break of serve to lead 2-0 in the decider and from there she used her power and experience to complete a nervy win.
She finished with a total of 43 unforced errors compared to just 16 for her opponent.