Nico Rosberg set the fastest time of a close final practice session which ended prematurely after an error by Pastor Maldonado.
Rosberg headed Felipe Massa, Sebastian Vettel and Fernando Alonso as the top four cars were covered by just 0.051s. Incidents started to occur in the closing stages of the session, however, and with three minutes to go Maldonado wiped the rear left wheel off his Williams after clipping the wall on the inside of Casino Square and sliding across the track.
Roberg's time of 1:15.159 was just 0.038s quicker than Massa, who chipped away at his best time as he looked more confident in the updated Ferrari. Vettel's lap came just before the red flag, but there could be more pace in the Red Bull as drivers seemed to find more time on their second and third flying laps on supersoft tyres.
Romain Grosjean was fifth quickest - 0.286s off Rosberg's best lap - with FP2 pacesetter Jenson Button just behind him in sixth place. Button was one of a number of drivers to complain of problems under braking, with the track taking a while to clean up having only seen limited use on Friday.
Drivers were building up confidence again having not driven the circuit since Thursday, with Vettel and Sergio Perez both tagging the barriers at the second part of the swimming pool. Timo Glock also required a front wing change after getting too close to the Armco, with matters not helped by traffic issues causing many flying laps to be aborted.
The session came to life in the final ten minutes as drivers pushed hard on supersoft tyres. First Perez was baulked by Nico Hulkenberg in the final corner, and then Hulkenberg's team-mate Paul di Resta lost the rear of his car over the bump under braking for the Nouvelle Chicane. Di Resta hit the barrier on the inside of the track with the nose of his car, but the damage was fairly limited and he was able to return to the pits.
Perez was then involved again as he backed off to allow Maldonado through before Portier. Inexplicably the Williams driver turned in early, making contact with the front of Perez's left tyre, before having his own accident that brought the session to a close one lap later.
Williams is left with a busy few hours to repair Maldonado's car ahead of qualifying, while teams will keep an eye on the skies with rain forecast to affect the session this afternoon.