Nico Rosberg lived up to expectations as the Mercedes driver set the pace in Thursday's first practice ahead of Fernando Alonso.
Arriving in Monaco many predicted that the Mercedes drivers would have the edge and that's exactly what Rosberg had on Thursday morning.
The German posted a 1:16.195 to beat Fernando Alonso by 0.087s while Romain Grosjean 0.185s down.
It was a slow start to the session as the dirty track kept the drivers in the pits with no times set during the first 30 minutes and just 32 laps from the entire field combined.
Esteban Gutierrez finally got the ball rolling with a 1:29.219 set in the 36th minutes of practice! He lowered the benchmark to a 1:24.130 before he was joined by Daniel Ricciardo, who took over at the front with a 1:19.753.
Felipe Massa was the first of the big boys to come out to play and immediately went quickest with a 1:18.818. Massa has never won the Monaco GP while his team-mate Fernando Alonso has two to his name.
Halfway through the session the top six were Massa, Ricciardo, Gutierrez, Jenson Button, Nico Hulkenberg and Kimi Raikkonen.
With more drivers heading out the times began to tumble. Massa improved his P1 time but lost out to Nico Rosberg who seconds later was pipped by Alonso by 0.163s. Lewis Hamilton took fourth on his first attempt while the Bulls were fifth and sixth with Sebastian Vettel ahead of Mark Webber.
A brief tussle between Rosberg and Alonso ensued as the duo traded fastest laps with Rosberg taking the honour with a 1:16.195. He was leading the way ahead of the final 30 with Alonso second ahead of Grosjean, who had a few moments of cutting the chican at the exit of the tunnel, Hamilton, Pastor Maldonado and Webber.
Alonso ventured out again and closed the gap on Rosberg to 0.087s while Massa climbed to third place. The Ferraris, though, just lacked that bit of extra pace to challenge the German. Meanwhile, Vettel was struggling to make his way up the order and was down in ninth.
The final few minutes, with the drivers on worn tyres, saw a few incidents with Adrian Sutil's spin the most notable. The Force India driver kissed the barriers with his rear wing as he spun around but appeared to escape without any damage.
Practice One ended with Rosberg quickest ahead of Alonso while a late dash from Grosjean put him third ahead of Massa and Hamilton.
The Bulls were seventh and tenth with Webber ahead while the McLarens finished eighth and ninth with Button edging Perez.
01 Nico Rosberg Mercedes 1:16.195 30 laps
02 Fernando Alonso Ferrari 1:16.282 +0.087s 26 laps
03 Romain Grosjean Lotus 1:16.380 +0.185s 20 laps
04 Felipe Massa Ferrari 1:16.394 +0.199s 22 laps
05 Lewis Hamilton Mercedes 1:16.469 +0.274s 27 laps
06 Pastor Maldonado Williams 1:16.993 +0.798s 26 laps
07 Mark Webber Red Bull 1:17.020 +0.825s 26 laps
08 Jenson Button McLaren 1:17.129 +0.934s 28 laps
09 Sergio Perez McLaren 1:17.378 +1.183s 24 laps
10 Sebastian Vettel Red Bull 1:17.380 +1.185s 22 laps
11 Kimi Raikkonen Lotus 1:17.509 +1.314s 25 laps
12 Paul di Resta Force 1:17.548 +1.353s 26 laps
13 Adrian Sutil Force 1:17.625 +1.430s 20 laps
14 Nico Hulkenberg Sauber 1:18.193 +1.998s 25 laps
15 Jean-Eric Vergne Toro Rosso 1:18.454 +2.259s 24 laps
16 Esteban Gutierrez Sauber 1:8.754 +2.559s 27 laps
17 Valtteri Bottas Williams 1:18.830 +2.635s 27 laps
18 Daniel Ricciardo Toro Rosso 1:19.067 +2.872s 24 laps
19 Giedo van der Garde Caterham 1:19.203 +3.008s 20 laps
20 Charles Pic Caterham 1:19.438 +3.243s 27 laps
21 Jules Bianchi Marussia 1:19.773 +3.578s 19 laps
22 Max Chilton Marussia 1:20.225 +4.030s 20 laps