Lewis Hamilton held off Max Verstappen, and survived a late collision with the Red Bull driver, to win a nail-biting Monaco Grand Prix.
The world champion was left struggling with the tyres on his Mercedes after fitting softer rubber than the Dutchman at pit stops during an early safety-car period.
Britain's Hamilton repeatedly complained that he was not going to be able to make the tyres last to the end but by careful management held on to take his fourth win of 2019.
Verstappen dropped from second on the road to fourth in the results because of a five-second penalty, promoting Ferrari's Sebastian Vettel to second and Mercedes' Valtteri Bottas to third.
Verstappen's punishment was for an unsafe release in the pits when all the leaders pitted on lap 12 as a safety car was deployed to clear up debris laid by Charles Leclerc's Ferrari.
Although Mercedes' run of consecutive victories at the start of this season continued, their sequence of one-twos is over as a result of Bottas' bad luck.
And Hamilton now holds a 17-point lead over his team-mate in the championship.