Fernando Alonso was fastest in first practice for the Monaco Grand Prix as the Ferrari driver ended the opening 90-minute session more than 0.3sec faster than the Lotus of Romain Grosjean.
Sauber driver Sergio Perez, returning to the scene of his frightening accident last year, was an impressive third fastest ahead of Lewis Hamilton, Spanish Grand Prix winner Pastor Maldonado and Felipe Massa.
There was the customary slow start to the session as teams were cautious of wasting tires on the "green" street circuit, leaving Jean Eric-Vergne and Toro Rosso teammate Daniel Ricciardo with the track mostly to themselves.
Vergne worked down to a 1m19.066s before some of the bigger names began to hit the track on the 40-minute mark. Those included Michael Schumacher's Mercedes and Romain Grosjean's Lotus. It was the Frenchman who would leave a lasting impression on the times as he first recorded a 1m17.645s to go quickest for the next 20 minutes until he was outdone by Alonso who lapped in a 1m17.126s – just as his teammate Massa scraped the barriers at Tabac.
The Ferrari ace's time stood for all of four minutes as the session passed through the hour mark and then Grosjean responded again with a 1m16.751s. This time it was Hamilton who bumped the Frenchman, putting McLaren top, going four thousandths quicker as the circuit began to get busy.
Once again Grosjean had an answer as he lapped in 1m16.630s only for Alonso to re-emerge from the pits with 15 minutes to go and fire in two super-quick laps, the first a 1m16.4s and the second an impressive 1m16.265s. That would prove enough.
The two-time World Champion had set an even faster first sector (19.8) as the session entered the final 10 minutes when Heikki Kovalainen's Renault engine failed through the tunnel stopping the session, the Caterham grinding to a halt on the exit and extinguishing all visibility from the area. The resultant oil on the track meant the session could not be restarted.
Behind the top six, Kamui Kobayashi was seventh for Sauber, ahead of Jenson Button's McLaren, world champion Sebastian Vettel and Nico Rosberg.
Five-time Monaco winner Schumacher ended up 11th after damaging his front wing when he clattered the kerbs at the Swimming Pool, while 2010 winner Mark Webber was 13th in the second Red Bull.
Kimi Raikkonen completed just a single installation lap before deciding the Monaco-specific steering wasn't to his liking and decided to have it changed, wiping out the rest of his session.
Pos Driver Team Time Laps
1. Fernando Alonso Ferrari 1m16.265s 22
2. Romain Grosjean Lotus-Renault 1m16.630s + 0.365 17
3. Sergio Perez Sauber-Ferrari 1m16.711s + 0.446 19
4. Lewis Hamilton McLaren-Mercedes 1m16.747s + 0.482 12
5. Pastor Maldonado Williams-Renault 1m16.760s + 0.495 20
6. Felipe Massa Ferrari 1m16.843s + 0.578 19
7. Kamui Kobayashi Sauber-Ferrari 1m17.038s + 0.773 21
8. Jenson Button McLaren-Mercedes 1m17.190s + 0.925 13
9. Sebastian Vettel Red Bull-Renault 1m17.222s + 0.957 14
10. Nico Rosberg Mercedes 1m17.261s + 0.996 18
11. Michael Schumacher Mercedes 1m17.413s + 1.148 14
12. Nico Hulkenberg Force India-Mercedes 1m17.631s + 1.366 18
13. Mark Webber Red Bull-Renault 1m18.106s + 1.841 14
14. Jean-Eric Vergne Toro Rosso-Ferrari 1m18.209s + 1.944 25
15. Daniel Ricciardo Toro Rosso-Ferrari 1m18.252s + 1.987 28
16. Paul di Resta Force India-Mercedes 1m18.302s + 2.037 16
17. Bruno Senna Williams-Renault 1m18.617s + 2.352 20
18. Heikki Kovalainen Caterham-Renault 1m19.03$s + 2.774 20
19. Vitaly Petrov Caterham-Renault 1m19.341s + 3.076 16
20. Narain Karthikeyan HRT-Cosworth 1m20.838s + 4.573 26
21. Charles Pic Marussia-Cosworth 1m20.895s + 4.630 18
22. Timo Glock Marussia-Cosworth 1m21.638s + 5.373 9
23. Pedro de la Rosa HRT-Cosworth 1m22.423s + 6.158 15
24. Kimi Raikkonen Lotus-Renault 1
All Timing Unofficial