It was first blood to Lewis Hamilton in Monaco practice while Nico Rosberg had the dubious honour of being the first to brush the barriers.
On a slightly damp Monte Carlo street circuit courtesy of overnight rain, the Mercedes were quickly into the action.
Putting in lap after lap after lap as many of their rivals bided their time in the pits, Hamilton and Rosberg attacked the circuit – and on at least one occasion got it a bit wrong.
Rosberg, who is chasing his third Monaco win this weekend, was the first to meet the Armco barriers, although only marginally. He brushed against the outside barrier at Tabac and immediately headed back into the pits.
While he was in the garage, Hamilton took control of the session leaving it to Rosberg to slowly work his way back up to the front when he returned to the action after his W06 had been given the all-clear.
With the track completely dry, the duo engaged in a brief battle for the P1 slot with Rosberg going quicker than Hamilton, Hamilton taking it back, Rosberg then edging him by 0.002s and finally Hamilton destroying his team-mate.
He posted a 1:19.196, lowered that to a 1:18.759 and then took a further 0.009s off that to finish quickest of all.
As expected the nature of the street circuit meant the order was mixed up but not many would have predicted Max Verstappen in second place.
The Toro Rosso rookie, a Monaco debutant, clocked a 1:18.899 to go second, 0.149s behind Hamilton.
Daniel Ricciardo put in a late run to work his way up to third, 0.336s off the pace, while their improvements meant Sebastian Vettel dropped to fourth ahead of Carlos Sainz. The duo were the final two drivers to get within half a second of the P1 time.
Pastor Maldonado, despite being one of many to take to the escape road at Ste Devote, finished sixth ahead of Daniil Kvyat, who was told to "calm down" when he complained about traffic late in the session, and Kimi Raikkonen.
Rosberg, who went with a heavier fuel load in the final 25 minutes, dropped to ninth with all the late climbers while Felipe Massa completed the top ten.
1 Lewis Hamilton Mercedes 1:18.750 49 laps
2 Max Verstappen Toro Rosso 1:18.899 0.149 42 laps
3 Daniel Ricciardo Red Bull 1:19.086 0.336 27 laps
4 Sebastian Vettel Ferrari 1:19.134 0.384 31 laps
5 Carlos Sainz Toro Rosso 1:19.245 0.495 40 laps
6 Pastor Maldonado Lotus 1:19.454 0.704 35 laps
7 Daniil Kvyat Red Bull 1:19.520 0.770 33 laps
8 Kimi Raikkonen Ferrari 1:19.679 0.929 31 laps
9 Nico Rosberg Mercedes 1:19.762 1.012 47 laps
10 Felipe Massa Williams 1:19.766 1.016 32 laps
11 Fernando Alonso McLaren 1:19.791 1.041 28 laps
12 Jenson Button McLaren 1:20.202 1.452 15 laps
13 Romain Grosjean Lotus 1:20.274 1.524 34 laps
14 Sergio Perez Force India 1:20.619 1.869 35 laps
15 Nico Hulkenberg Force India 1:20.784 2.034 34 laps
16 Felipe Nasr Sauber 1:20.857 2.107 24 laps
17 Valtteri Bottas Williams 1:20.917 2.167 36 laps
18 Marcus Ericsson Sauber 1:21.219 2.469 25 laps
19 Will Stevens Manor 1:23.234 4.484 28 laps
20 Roberto Merhi Manor 1:23.404 4.654 31 laps