Daniel Ricciardo topped the times ahead of his Red Bull team-mate Max Verstappen in Thursday’s opening free practice for this weekend’s Monaco Grand Prix.
The big-smiling Australian clocked a best lap of one minute and 12.126 seconds to outpace the young Dutchman by one-tenth of a second.
Championship leader and defending four-time champion Briton Lewis Hamilton was third for Mercedes, three-tenths adrift of the quickest time, ahead of title rival and fellow four time champion German Sebastian Vettel of Ferrari.
Finn Kimi Raikkonen was fifth in the second Ferrari ahead of Spaniard Carlos Sainz of Renault and Finn Valtteri Bottas who was seventh in second Mercedes.
Mexican Sergio Perez was ninth for Force India ahead of a controlled Frenchman Romain Grosjean of Haas and Russian rookie Sergey Sirotkin of Williams, who bounced back from an early skirmish.
On a bright clear blue-skied morning in the Mediterranean principality, Mercedes were quickly into their stride with both men topping the times in the opening minutes before Red Bull joined the fray in earnest.
Thereafter it was cut and thrust between the two teams in a session of few incidents – Sirotkin clipping the barriers and damaging the right rear wheel of his Williams and Fernando Alonso being sidelined for repairs to a braking issue.
The Spaniard returned to wind up 17th.
As many expected, including Hamilton, the Red Bull drivers revelled in the handling of their car on the tight and unforgiving street track as both Verstappen and Ricciardo topped the times using the new ‘hyper-soft’ tyres on the resurfaced track.