With the clouds closing in on Roland Garros, Stosur survived a tense tiebreak to prevail 6-4 7-6 (8-6) in a little under two hours and advance to the final four for the fourth time – adding to a 2010 defeat in the final and semi-final exits in 2009 and 2012.
“I think typically whoever wins a grand slam, they don’t always play their best tennis every single day, but they find a way to win,” said Stosur, who will rise to at least 14 in the world following the win.
“That’s what I was able to do today.”
Stosur will next play fourth seed Garbine Muguruza on Friday for a spot in Saturday’s final, with the Spaniard downing American outsider Shelby Rogers in straight sets.
“She hits the ball hard and flat. It’s going to be hard,” Stosur said.
The women on the other side of the draw – including world No.1 and favourite Serena Williams – will play their quarter-finals on Thursday as organisers attempt to reorganise the schedule following many rain delays.
Stosur started slugglishly in the cool conditions overnight, Australian time, and was twice broken in her opening three service games to go down 4-2 in an error-strewn opening to the match.
She was on the cusp of being broken again, giving up triple break point which would’ve seen her go 5-2 down and on the edge of conceding the first set.
However Stosur would save all three – letting out a motivating “c’mon” in the process – in a game which would prove the match’s turning point.
Stosur would win the next five games as her rhythm returned, closing out the first set in 41 minutes.
“Obviously that was a big moment. 5-2 is a hell of a lot different to 4-3,” Stosur said.
“And then it’s probably even more so when they have just had three break points and really almost feel like they are in total control of the match.
“That was a really crucial part of the match.”
With her head clear, Stosur returned to the sort of form which helped take down the past two beaten French Open finalists, Lucie Safarova and Simona Halep.
However with her French Open on the line, Pironkova responded to break Stosur early in the second and open up a 3-1 lead.
Stosur then won three games on the bounce to regain control of the set.
As clouds darkened and rain threatened to return, Stosur was able to ice the quarter-final by fighting back from 1-5 in the tiebreak.
After saving two set points, Stosur forced an error from the Pironkova forehand to take the win and the semi-final berth.
Pironkova applauded the career renaissance of her Australian rival, saying age won’t be a factor as Stosur sets her sights on a French Open triumph.
At 32, Stosur is the second oldest remaining in the women’s draw – with only the unrivalled 34-year-old Serena Williams her senior.
Williams holds the record, at 33 years and 289 days, as the oldest female grand slam winner – something she achieved at Wimbledon last year for her 21st grand slam title.
But despite being 10 years the senior of her semi-final opponent, Spanish fourth seed Garbine Muguruza, Stosur remains at the peak of her fitness and says she’s moving around the court as well as ever.
And having been dusted in straight sets, Pironkova gave her every chance of adding a French Open title to her 2011 US Open silverware.
“Yeah, sure. Why not?” the 28-year-old said.
“I don’t think age is a factor that much anymore.
“Obviously players are playing until much older age than they used to be playing.
“She looks fit. She’s playing well. She’s hitting well. She’s fighting till the end.
“She’s playing semi-finals now, so obviously she has her chances.”
Pironkova hailed Stosur’s fighting qualities and said the variety in her game – coupled with a fearsome forehand and near-flawless overhead smash – made her a difficult matchup for any opponent.
“Her strokes are not typical. They jump really high,” she said.
“She’s also playing on the net. She’s doing slice shots, great serve, great overhead. She didn’t miss a single overhead.”
Despite her hot form and being just four sets away from potentially lifting the Suzanne Lenglen Cup, Stosur will not let herself think about taking out the title just yet.
Her semi-final will be against world No.4 Muguruza, another tough proposition, and that is as far as Stosur will let her mind wander.
“There’s four of us left out of 128 – (so I’m a) 25 per cent chance of winning at the moment,” Stosur laughed.
“You can’t get ahead of yourself. I’m not thinking anymore about being in that position as what I was before I played my first round, to be honest.
“I know that this next match is going to be very hard.
“There are only a handful of us left now and we all want it really bad.
“It’s not going to be easy from this point on.”
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