Gilles Simon of France staged an upset on the first day of the Croatia Open ATP tournament on Monday by beating world number four Nikolay Davydenko of Russia 6-2 2-6 6-3.

The 22-year-old Frenchman has one singles title to his name, won earlier this year in Marseille and reached the quarter-finals of the Bastad tournament last week.

Top seed and world number three Novak Djokovic from Serbia had an easier passage to the second round, beating Spaniard Pablo Andujar 6-1 6-3.

Two other Spaniards, Pere Riba and Ruben Ramirez Hidalgo, managed to stay in the tournament by beating local youngster Luka Belic 6-2 2-6 6-4 and Gaston Gaudio of Argentina 6-0 6-4.

Local hope Marin Cilic overcome Frenchman Mathieu Montcourt 3-6 6-4 6-1, while Argentine Carlos Berlocq beat his compatriot Maximo Gonzalez 6-3 6-4. Cilic will meet Simon in the second round.