Home favourite Matteo Berrettini beat world number five Alexander Zverev of Germany in the second round of the Italian Open in Rome.
The Italian, 33rd in the Association of Tennis Professionals (ATP) rankings, won 7-5, 7-5 at Foro Italico.
Andrea Basso could not emulate his compatriot's feat, losing 6-1, 7-5 to Croatia's Marin Čilić.
Unseeded Nick Kyrgios of Australia pulled off an upset against Daniil Medvedev, defeating the Russian 6-3, 3-6, 6-3.
In the Women's Tennis Association Premier 5 event, Serena Williams of the United States and Caroline Wozniacki of Denmark both withdrew due to injury.
Williams had been set to play her sister Venus, while Wozniacki retired during her match against American Danielle Rose Collins.
In other fixtures, Australia's Ashleigh Barty battled through against Slovakia's Viktória Kužmová, eventually winning 4-6, 6-3, 6-4.
Czech Karolína Plíšková eased past Barty's compatriot Ajla Tomljanović 6-3, 6-3.
The men and women's competitions continue tomorrow.