Nico Rosberg took a surprise hat-trick of Monaco Grand Prix victories on Sunday after Mercedes blew championship-leading team mate Lewis Hamilton's chances with a late pitstop while he was in the lead.
The result, with Hamilton third after leading for 64 of the 78 laps after starting on pole, slashed the Briton's lead over German rival Rosberg to 10 points after six of the 19 races this year. Ferrari's Sebastian Vettel finished second.
Hamilton's race unravelled when the safety car was deployed after Dutch 17-year-old Max Verstappen crashed heavily into the barriers.
Rosberg trailed championship-leading Mercedes team-mate defending champion Lewis Hamilton for 63 laps until an accident prompted a Safety Car intervention that, in turn, led the team to call the Briton in for an unexpected and unnecessary pit-stop.
Obeying his team, Hamilton, who led by 21 seconds before he pitted, came out in third place and, after the race was re-started with eight laps remaining, found it impossible to pass Sebastian Vettel's Ferrari, let alone Rosberg, to claim his fourth victory of the year.
"I've lost the race haven't I," the disconsolate double Formula One world champion enquired over the team radio after rejoining in third place. "What's happened guys?"
For the two-time champion, it was an outrageous result. His team were swift to apologise for it, but their actions had deprived him, and the spectators, of a fair sporting outcome after he had dominated the 62nd running of this classic 78 laps contest.
Rosberg's triumph enabled him to join Briton Graham Hill, Frenchman Alain Prost and Brazilian Ayrton Senna in completing a Monaco hat-trick. It was also his second win in a row, following his victory in Spain, and rekindled his challenge for the drivers' championship.
Up until the Safety Car was deployed, it had been Hamilton's race, but he ended up settling for a disappointed third ahead of the two Red Bulls of Russian Daniil Kvyat and Australian Daniel Ricciardo.
Finn Kimi Raikkonen finished sixth for Ferrari ahead of Mexican Sergio Perez of Force India and Briton Jenson Button who claimed the struggling McLaren Honda team's first points of the year in eighth place.
Brazilian Felipe Nasr came home ninth for Sauber and remarkably, after starting from the pit lane, Spaniard Carlos Sainz finished 10th to score a point in the second Toro Rosso car.