Lewis Hamilton fastest in Monaco practice
Lewis Hamilton headed title rival Sebastian Vettel in first practice at the Monaco Grand Prix as Jenson Button finished 14th on his return to F1.
Hamilton's Mercedes led Vettel's Ferrari by 0.196 seconds as Red Bull's Max Verstappen took third from the second Mercedes of Valtteri Bottas.
Hamilton spent the first part of the session swapping fastest times with Bottas but edged clear by 0.366secs.
Button ended up 0.141secs off the pace of McLaren team-mate Stoffel Vandoorne.
The 2009 world champion is standing in for Fernando Alonso while the Spaniard is racing in America at the Indianapolis 500 this weekend.
Button, who has moved to California and has spent the time since his retirement at the end of last season training and qualifying for the triathlon world championships, played himself in gently with a long run on the soft tyres before moving on to the popular ultra-soft, on which most running will be done this weekend.
He had not driven the car before this weekend, eschewing the chance to test in Bahrain in April because he felt it would be useless.
At the front, Mercedes appear to have a small edge on Ferrari at this early stage and Red Bull look to have taken a further step towards the top two teams after progress at the last race in Barcelona.
Verstappen damaged his car and needed repairs in the middle of the session but was sent back out again to end up 0.346secs off Hamilton's pace.
Red Bull said Verstappen had damaged his car's floor, probably by bouncing over the kerbs at the fast left-right at the Swimming Pool. When he was sent back out again, he ended up 0.346secs off Hamilton's pace.
His team-mate Daniel Ricciardo was fifth quickest, 0.083secs behind the Dutchman.
Toro Rosso's Daniil Kvyat was sixth fastest using the harder super-soft tyre, with Ferrari's Kimi Raikkonen seventh.