Daniil Medvedev has been the subject of a major upset in the French Open first round.
Brazilian qualifier Thiago Seyboth Wild - ranked 172 in the world - has beaten Medvedev in five sets.
Already today there have been wins for fourth seed Casper Ruud and Alexander Zverev.
Women’s fourth seed Elena Rybakina beat Brenda Fruhvirtová in straight sets, and will face another Czech - Linda Noskova in round-2.
Still to come, top seed Iga Swiatek begins the defence of her title against Cristina Bucsa.
2021 champion Barbora Kreijcikova lost in straights to Lesia Tsurenko.
But there have been wins for sixth and seventh seeds Coco Gauff and Ons Jabeur.