Mercedes driver Nico Rosberg controlled an incident-packed Monaco Grand Prix from start to finish, winning the event 30 years after his father Keke triumphed in the famous street race.
However, the race was clouded by a row that erupted over a secretive tyre test that Mercedes conducted with Pirelli after the previous race in Spain. The German squad's key rivals Red Bull and Ferrari have lodged a protest because Mercedes used its 2013 car for the tyre test, which they see as a contravention of the sporting regulations.
On track, Mercedes continued its impressive one-lap pace in qualifying and Rosberg and team-mate Lewis Hamilton shut-out the front row ahead of the Red Bulls of Sebastian Vettel and Mark Webber.
Come the race, Rosberg and Hamilton managed to hold first and second places into the opening right-hander, Sainte Devote, on the opening lap, with the Briton resisting fierce pressure from an eager Sebastian Vettel.
Further back McLaren twins Jenson Button and Sergio Perez almost came to blows, with the Mexican twice having to cut across corners in a bid to stay ahead of the 2009 world champion. His moves prompted Button to complain about his team-mate over the car-to-pit radio, and the team took the decision to tell Perez to cede position to Button.
The race remained static as the top runners conserved their tyres and the fact that the field remained very tightly bunched prompted most of the leading protagonists to switch from a planned two-stop to a one-stop strategy. Top ten runners Webber, Fernando Alonso, Kimi Räikkönen and Jenson Button had all made their stops when Ferrari's Felipe Massa had a massive accident at Sainte Devote, precipitating a safety car period. The Brazilian was shaken in the crash, which was very similar to one he had in practice on Saturday.
Vettel was changing tyres at the moment that the safety car was being deployed, but the two Mercedes drivers at the head of the field had to come in on the next tour. Although Rosberg was able to rejoin in the lead, Hamilton, who had to slow down on his in-lap to give the pit crew time to get ready after they'd dispatched the German, lost track position to both Vettel and Webber.
When the race resumed, Rosberg inched away from the Red Bull twins as Hamilton attacked Webber and behind them Räikkönen came under severe pressure from Alonso. But the Spaniard was caught napping by a feisty Perez, who had retaken seventh place from team-mate Button under braking for the chicane, and tried the same move on Alonso. The Ferrari man drove across the run-off area to retain sixth position, but was later told by officials to cede the position to his Mexican rival.
Then the red flag came out on lap 46 when Max Chilton and Pastor Maldonado tangled and the Venezuelan slammed into the barriers, before Chilton's team-mate Jules Bianchi got caught up in the aftermath. The cars reformed on the grid for the restart and were permitted to change tyres, alleviating concerns about tyre wear among the leaders.
When the race got going again, it took Rosberg little time to re-establish his lead over the chasing Red Bulls, while fourth-placed Hamilton complained off severe graining to his front tyres.
A driver on the move was Adrian Sutil, who pulled an opportunist move on Button at the hairpin for eighth place, then did the same to Alonso for seventh a few laps later. Alonso had picked up some debris on his front wing, which compromised his Ferrari's handling.
