Serena Williams through after Magdalena Rybarikova win as Victoria Azarenka and Angelique Kerber crash out of French Open
Serena Williams easily beat hampered Magdalena Rybarikova 6-2 6-0
A knee injury forced Victoria Azarenka to retire trailing Karin Knapp
Kiki Bertens defeated Angelique Kerber with a 6-2 3-6 6-3 victory
Eugenie Bouchard eased past dangerous Laura Siegemund 6-2 6-2
But in the first round of the tournament she saw arguably the two biggest potential dangers removed from her path.
Azarenka looked back to something like the form that made her Williams' biggest challenger before injury problems struck when she won both Indian Wells - beating the world No 1 in the final - and Miami in March.
But again physical frailties have proved her undoing and, after back problems earlier in the clay season, a right knee injury forced her to retire trailing Italy's Karin Knapp 6-3 6-7 (6/8) 4-0.
Azarenka seemed unlikely to make it that far when she first received treatment at 3-3 in the second set but she carried on playing and saved a match point in the second-set tie-break.
However, in the third set the wheels came off and she was in tears before finally deciding to call it a day.
Australian Open champion Kerber became the highest-ranked casualty of the tournament so far when she was beaten by Kiki Bertens.
It was a tough draw for the third seed, with Bertens going into the clash on the back of a title in Nuremberg at the weekend, and the Dutchwoman continued her fine form to win 6-2 3-6 6-3.
The leading women have been hugely inconsistent all season so it is no great surprise to see a couple of them fall early.
Kerber, who has been struggling with a shoulder problem, said: 'I was ready. I was practising very well here, but the first rounds are always tough in the tournament, especially for me. What can I say? It happens.
'I tried to fight in the third set. But she played well in the important moments.'
Eugenie Bouchard is now down at 47 in the rankings but her form of late has been a little more encouraging and she eased past dangerous German Laura Siegemund 6-2 6-2.
Bouchard had a nightmare season in 2015 after reaching the top 10 the previous year and found the whole experience so stressful it led to an eating disorder.
She said: 'I felt a lot of pressure and kind of this expectation that if you win a match it's normal and if you lose it's a disaster.
'Before matches I was very nervous and definitely had trouble eating. I just felt like it would come right back up. It's a difficulty I went through. And not just before matches, but it happened to me at other meals as well.
'So people think I was concerned about my body image and things like that and I was losing weight on purpose. That was really not the case. I was just so stressed.'
In the next round Bouchard will play last year's semi-finalist Timea Bacsinszky. The eighth seed is one to watch and defeated Silvia Soler-Espinosa 6-3 6-1.
Ninth seed Venus Williams won only her second match at Roland Garros in the last four years, beating Anett Kontaveit 7-6 (7/5) 7-6 (7/4).
Williams' fellow 35-year-old Francesca Schiavone had to deny she was retiring after Roland Garros' Twitter feed mistakenly announced this as her final appearance.
The Italian, who won the title in 2010 and reached the final again the following year, was given a prolonged ovation after her 6-2 6-4 loss to France's Kristina Mladenovic.
'I appreciate this situation,' said Schiavone. 'But I think that everybody thought this because Roland Garros announced it. It was not the last one for me.'
Former champion Ana Ivanovic, Andrea Petkovic, Carla Suarez Navarro and Madison Keys all reached round two but Jelena Jankovic is out.
Canadian Bouchard, who is now 22 years old, eased past dangerous German Laura Siegemund 6-2 6-2
