Mercedes driver Nico Rosberg posted the fastest time in the first practice session of the Monaco Grand Prix on Thursday.
The German driver has been on pole position for the last two races and clocked 1 minute, 16.195 seconds to finish 0.087 faster than Ferrari rival Fernando Alonso.
Alonso won the Spanish GP two weeks ago and is looking to become the first driver to win in Monaco with three different teams. Romain Grosjean was third fastest for Lotus.
Although Mercedes has been fastest in qualifying for the last three races, Rosberg and teammate Lewis Hamilton have yet to win a race.
Hamilton, who took pole at the Chinese GP, was fifth behind Ferrari driver Felipe Massa.
Championship leader Sebastian Vettel was 10th ahead of Thursday's second practice run.