Defending champion Maria Sharapova reached the French Open last 16 on Friday but appeared on the verge of tears at the end of her straight-sets win over Samantha Stosur.

The world No.2 made the fourth round for the 11th time with a 6-3 6-4 win over the 26th-seeded Australian.

It was the Russian’s 15th win in 17 matches against Stosur, who she edged in a tight three-setter in Paris last year.

Sharapova admitted that her continuing struggles with a cold, which saw her coughing for large parts of the match, contributed to her emotional state at the end.

“I have never felt like that on the court playing a grand slam, so this is kind of new,” said the 28-year-old.

“I’m just trying to do the best that I can with the circumstances.”

Sharapova, also the champion in 2012 and runner-up in 2013, goes on to face 13th seed Lucie Safarova for a place in the quarter-finals.

Safarova made the fourth round for the third time by beating big-serving German Sabine Lisicki 6-3 7-6 (7-2).

Sharapova has a 4-1 record over the 28-year-old Czech, whose only win came in the pair’s first meeting in Madrid five years ago.

However, their last clash in Stuttgart in 2014 only went in the Russian’s favour after three tiebreak sets.

Former champion Ana Ivanovic reached the last 16 in just 53 minutes.

The Serbian seventh seed, the 2008 winner in Paris, triumphed over 18-year-old Croatian opponent Donna Vekic 6-0 6-3.

Ivanovic, watched by German football star boyfriend Bastian Schweinsteiger, swept into a fourth round clash against ninth-seeded Russian Ekaterina Makarova.

Makarova reached the last-16 for the second time by defeating doubles partner Elena Vesnina 6-2 6-4.

“I hate having to play my best friend,” admitted the 26-year-old left-hander. “It’s not a good feeling.”

Alize Cornet, the 29th-seeded Frenchwoman, needed two and a half hours to defeat 33-year-old Croatian Mirjana Lucic-Baroni 4-6 6-3 7-5 in a match scarred by 85 unforced errors.

Lucic-Baroni made her Paris debut back in 1999 and had made the last 32 by putting out third-seeded Simona Halep in the second round.

Cornet, who knocked Serena Williams out of Wimbledon last year, will be playing in the second week in Paris for the first time.

“It’s magical,” said Cornet, who next takes on Elina Svitolina, the 19th-seeded Ukrainian contesting a fourth round of a major for the first time.

Svitolina defeated fellow former French Open junior champion Annika Beck of Germany 6-3 4-6 6-4.

Spanish 21st seed Garbine Muguruza, who beat Williams on her way to the quarter-finals in 2014, knocked out German 11th seed Angelique Kerber 4-6 6-2 6-2.

She will face Italian veteran Flavia Pennetta who defeated two-time quarter-finalist Carla Suarez Navarro 6-3 6-4 in a tie which featured 12 breaks of serve.

Suarez Navarro’s defeat means that five of the top 10 seeds have now been knocked out.