Alonso leads in practice 1

Hamilton was the early pacesetter, his 1:18.686 effort after 23 minutes being 1.5 seconds quicker than teammate Alonso's first flying lap.

However, the 22-year-old had completed just 14 laps of the tight and twisty street circuit before he was sidelined in the pits by a broken starter motor.

The team said a piece of debris had been left in the gearbox, forcing mechanics to remove the floor of the car to fix the problem.

That gap was soon cut to 0.4 seconds when the session resumed following a brief red flag while Christijan Albers' Spyker which retrieved from Tabac, where it had ground to a halt.

Massa then usurped Hamilton momentarily with a 1:18.537 lap, but his superiority was fleeting, for the Briton replied with a 1:17.601 almost immediately.

Despite both Massa and Alonso improving their times, Hamilton maintained a six tenths of a second advantage until his teammate bolted on a set of super-softs on the one-hour mark and lapped in 1:16.973, 0.628 seconds clear of the field.

The leading positions remained static for the final half hour, but the Ferraris were pushed down to fifth and eighth as others made late improvements.

BMW's Nick Heidfeld, who had earlier abandoned a fast lap after a wild trip across the chicane kerbs, ended up third, ahead of Renault's Giancarlo Fisichella.

But moments after setting the fourth fastest time, Fisichella went straight on into the Sainte Devote barrier after clipping the inside kerb too heavily, ending his session.

Kimi Raikkonen finished practice in fifth place, with teammate Massa down in eighth, demoted by Mark Webber and Nico Rosberg in the closing moments. Webber then slowed with a left rear puncture after setting his fast lap.

Robert Kubica and Rubens Barrichello completed the top ten, while Scott Speed got as high as eighth for Toro Rosso before falling to 12th behind Alex Wurz.

Pos  Driver        Team                    Time              Laps
 1.  Alonso        McLaren-Mercedes   (B)  1:16.973            33
 2.  Hamilton      McLaren-Mercedes   (B)  1:17.601  + 0.628   14
 3.  Heidfeld      BMW Sauber         (B)  1:17.616  + 0.643   31
 4.  Fisichella    Renault            (B)  1:17.758  + 0.785   27
 5.  Raikkonen     Ferrari            (B)  1:17.918  + 0.945   28
 6.  Webber        Red Bull-Renault   (B)  1:17.956  + 0.983   19
 7.  Rosberg       Williams-Toyota    (B)  1:18.074  + 1.101   27
 8.  Massa         Ferrari            (B)  1:18.189  + 1.216   29
 9.  Kubica        BMW Sauber         (B)  1:18.675  + 1.702   28
10.  Barrichello   Honda              (B)  1:18.676  + 1.703   22
11.  Wurz          Williams-Toyota    (B)  1:18.869  + 1.896   29
12.  Speed         Toro Rosso-Ferrari (B)  1:18.967  + 1.994   27
13.  Coulthard     Red Bull-Renault   (B)  1:19.095  + 2.122   16
14.  Sato          Super Aguri-Honda  (B)  1:19.203  + 2.230   27
15.  Liuzzi        Toro Rosso-Ferrari (B)  1:19.285  + 2.312   24
16.  Kovalainen    Renault            (B)  1:19.321  + 2.348   27
17.  Button        Honda              (B)  1:19.332  + 2.359   27
18.  Davidson      Super Aguri-Honda  (B)  1:19.337  + 2.364   22
19.  Trulli        Toyota             (B)  1:19.496  + 2.523   22
20.  R.Schumacher  Toyota             (B)  1:19.799  + 2.826   25
21.  Sutil         Spyker-Ferrari     (B)  1:21.634  + 4.661   19
22.  Albers        Spyker-Ferrari     (B)  1:23.235  + 6.262    5