MONACO (Reuters) - Formula One world champion Lewis Hamilton set the pace in an incident-filled opening Monaco Grand Prix practice on Thursday, with debris and a loose drain cover bringing an early end to the session.

The Briton, who trails his championship leading Mercedes team-mate Nico Rosberg by 43 points after five races and collided with the German in Spain 11 days ago, lapped the sinuous street circuit in one minute 15.537 seconds.

Rosberg, winner for the past three years in the principality, was second fastest in 1:15.638 on the new ultrasoft tyres.

Ferrari's Sebastian Vettel was third fastest, four tenths slower, followed by the Red Bulls of Australian Daniel Ricciardo and Dutch 18-year-old Max Verstappen.

Brazilian Felipe Massa provided the first incident when he skewed his Williams into the barriers at the first Sainte Devote corner before the uphill sweep to Casino Square, leaving plenty of work for his unimpressed mechanics.

That smash, with 24 minutes gone, triggered the virtual safety car.