Samantha Stosur knows all about tennis turnarounds.

The 2011 US Open champion says 108th-ranked Shelby Rogers' dream run to her first career Grand Slam quarterfinal at Roland Garros is a reminder of how fast careers can be transformed in tennis.

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"I think you've always got to be ready. Tennis is something, it can change quickly," Stosur said after defeating Simona Halep to reach the quarterfinals. "I was reading the other day, Shelby Rogers, she lost in qualifying in Strasbourg and now she's in the quarters. One tournament to the next, smallest tournament on tour and the biggest one. She's had polar opposite results. Shows how quickly things can turn around.

"Also, the margins are so small. You can make big changes very quickly if you're prepared to, you know, take them."

The 21st-seeded Stosur was an agent of change today.

Trailing Halep 3-5 in a clash of former French Open finalists, Stosur ralllied for a 7-6 (0), 6-3 victory to reach her fourth French Open quarterfinal. She will be favored to reach the semifinals when she takes on world No. 102 Tsvetana Pironkova, who upset second-seeded Agnieszka Radwanska.

It is Stosur's first Grand Slam quarterfinal appearance since the 2012 US Open.

Recalling past success in the City of Light has sparked Stosur in her run to the second week.

"I think most careers of some of the greatest players in the world or ever always have ups and downs," Stosur said. "And I think it is important to know, Okay, even if you're having a period, a bit of a slump, what you have been able to achieve beforehand it doesn't all just go away. If you've done it there for a consistent period then you can you get it back again.

"You have to put all these things back together and make it work. So, I mean, it sounds really simple. Staying positive and working hard can take you a long way. You have just got to always wait for that breakthrough and opportunity to arise. Sometimes it takes longer and sometimes it can happen a lot quicker."