MONACO Formula One world champion Lewis Hamilton set the pace in an incident-filled opening Monaco Grand Prix practise 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.
Verstappen, who became Formula One's youngest race winner in Spain, will be using an older specification Renault engine than Ricciardo in Sunday's showcase race around the picturesque harbourside track.
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.
Mexican Esteban Gutierrez set it off again with half an hour remaining when he stopped his Haas before Portier with electrical problems, and then Renault's British rookie Jolyon Palmer crashed at Tabac.
"Sorry, guys," Palmer said over the radio.
Yellow warning flags were waved when Brazilian Felipe Nasr's Sauber went off at Sainte Devote and the virtual safety car was deployed for the third time when Rosberg's car suffered damage and a rear left puncture at Sainte Devote.
Television replays indicated a manhole cover had lifted, confirmed later by Mercedes, with McLaren's Jenson Button then running over it and debris from the Mercedes.
The McLaren suffered a puncture and damaged front wing, with the session stopped and the final two minutes of the session abandoned.
Track workers were then deployed to Sainte Devote to weld down the offending cover.