Red Bull's Daniel Ricciardo overcame a mid-race power loss to win the Monaco Grand Prix from pole position on Sunday.
The Australian driver showed outstanding composure and defensive driving to fend off Sebastian Vettel's Ferrari.
Hamilton's championship lead cut to 14 points
Vettel shaved a few points off championship leader Lewis Hamilton of Mercedes, who finished third.
Hamilton made an audacious move by pitting for new tires several laps before his rivals, but was worried they would wear out completely by the end.
The virtual safety car came out for the last few laps after Charles Leclerc lost his brakes and shunted his Sauber into the back of Brendon Hartley's Toro Rosso. Drivers are not allowed to overtake when the VSC is deployed and must maintain a steady speed.
The incident came too late and made no difference to the overall race picture.
Kimi Raikkonen was fourth for Ferrari ahead of Mercedes' Valtteri Bottas and Force India's Esteban Ocon.