Li ousts Stosur as Wawrinka crashes in Rome
Li Na of China returns the ball to Samantha Stosur of Australia during a Rome Masters tennis match at the Foro Italico in Rome on May 15, 2014 - by Andreas Solaro
Stosur, a 2010 Roland Garros finalist, had beaten world number two Li in all six of their previous meetings going back to 2007.
The victory was her second straight over an Aussie opponent after defeating qualifier Casey Dellacque in the previous round.
But China's top female athlete made inroads against Stosur's one-way scoreline with her first victory, achieved in 68 minutes with five breaks of the 30-year-old Australian.
In the last six matches I tried to control the ball, but she was able to get a lot of chances," said 32-year-old Li. "I'm just trying to focus now on every match I play."
Li will play a quarter-final against Italian tenth seed Sara Errani, who beat Czech Petra Cetkovska 6-3, 7-6 (7/3).
"Errani will be tough as she will have the crowd on her side and plays well on clay."
Li finished Rome runner-up in 2012, holding a match point against eventual champion Maria Sharapova.
Australian Open champion Li is looking for her third trophy of the season as she prepares for the French Open, which she won in 2011.
Men's third-seeded Monte Carlo winner Stanislas Wawrinka joined fellow Swiss Roger Federer on the Rome scrapheap after a 5-7, 6-2, 6-3 loss to German 15th seed Tommy Haas.
The 36-year-old has now won both of his matches with Wawrinka, a 2008 finalist at the Foro Italico.
Haas ended with seven aces to eight for Wawrinka, who could not hold onto leads throughout the two-hour contest.
The German produced 32 winners while Wawrinka struck 40 unforced errors.
Haas broke in the third set for 5-3, then finished with an ace a game later on his first match point.