Federer returned to the French Open's third round with a predictably straightforward 6-4, 6-3, 6-4 victory over 144th-ranked Oscar Otte.
Rohan Bopanna and Marius Copil beat sixth-seeded Michael Venus and Raven Klaasen in straight sets to advance to the second round at Roland Garros.
Serena Williams came back from one-set down to defeat 83rd seed Vitalia Diatchenko. Petra Kvitova, however, had to pull out of the tournament with an injury.
Rafael Nadal entered the second round at Roland Garros, but former World No.1 Caroline Wozniacki was stunned by 68th-ranked Veronika Kudermetova.
Venus lost her opening match at Roland Garros for the second year in a row, beaten 6-3, 6-3 by ninth-seeded Elina Svitolina in 1 hour, 13 minutes.
Angelique Kerber lost 6-4, 6-2 to an 18-year-old Roland Garros beginner, Russian Anastasia Potapova, on Court Philippe Chatrier.
The defending champion was handed what looked like quite an easy draw on Thursday at Roland Garros stadium, where the Spanish player attended the ceremony and said he was happy with his form.
Nick Kyrgios has pulled out of the tournament, but no official reason has been given by the player yet.
Asked who would end up winning most number of titles in men's singles, Sanchez said it is difficult for her to pick one because Roger Federer, Rafael Nadal and Novak Djokovic are great players and equally competent.
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