Lewis Hamilton set the fastest ever lap of the Monaco Grand Prix circuit, on his way to topping First Practice, just 0.196s clear of Ferrari's Sebastian Vettel.
The Mercedes driver set the pace in the opening session of Formula 1's, flag-ship event, lapping on ultra-soft Pirelli tyres in 1:13.425s.
Behind the two title rivals, Max Verstappen suffered from a disrupted session, but still managed to be third quickest, despite losing a chunk of time when Red Bull needed to change his floor after he damaged it.
Valtteri Bottas and Daniel Ricciardo were fourth and fifth quickest, with Danill Kvyat slotting the Toro Rosso into sixth place, ahead of Kimi Raikkonen.
Both Force India's made it into the Top 10, with Carlos Sainz being the meat in it's sandwich, with Sergio Perez and Esteban Ocon finishing either side of the Spanish driver.
On his return, Jenson Button was slightly cautious in his first session in the MCL32, ending up a respectable 14th place.
Early laps on the board
From the out-set, drivers were putting times on the board, with Bottas going for a four lap stint immediately and setting the benchmark on super-soft Pirelli's, until Vettel came through and trumped the Finn's best efforts.
Verstappen's early running was curtailed when Red Bull radioed to him that it suspected he had a "right-rear puncture" and the young Dutchman came into the pits.
The RB13 actually suffered floor damage after a moment at Turn's 12 and 13, and he lost the momentum he built up after the quickest first sector at that point.
Button was focusing his running on the Soft tyre, doing so to help him bed in, and adjust to the new car. He did an adequate job, although did complain of a lack of grip and locked-up on his out-lap at Tabac.
With just over half the session remaining, the switch to ultra-softs initially saw Hamilton and Bottas trading fastest laps, with the Brit coming out on top, with the fastest ever lap in Monaco, the 1:13.425s that saw him top the session.
Interestingly, both Toro Rosso drivers set their times on the slower super-soft tyre, although they may have played with the fuel loads, but to be within a second on the slower tyre was a good effort from both drivers.
Owing to the big kerb on the exit of the Swimming Pool, drivers were forced to take a shallower line into the entry of the second chicane of the section, with Raikkonen, Vettel and Perez all giving the barrier on the inside a hefty whack.
Elsewhere, it was a quiet FP1, with only Romain Grosjean's spin at Sainte Devote on his way to 15th place the only major incident of note as drivers bedded themselves into the track.
Nico Hulkenberg and Marcus Ericsson failed to set a flying lap time, the Renault falling foul of an ERS problem, while Swede Ericsson's Sauber lost fourth gear in the early part of the first 90 minutes of on-track action.
|3.||Max Verstappen||Red Bull||+0.346|
|5.||Daniel Ricciardo||Red Bull||+0.429|
|6.||Danill Kvyat||Toro Rosso||+0.686|
|8.||Sergio Perez||Force India||+0.776|
|9.||Carlos Sainz Jr||Toro Rosso||+0.908|
|10.||Esteban Ocon||Force India||+1.000|
|19.||Nico Hulkenberg||Renault||No Time|
|20.||Marcus Ericsson||Sauber||No Time|