Third fastest, almost half a second behind Webber, was Felipe Massa, whose position at Ferrari is under intense scrutiny as the season reaches its climax.
Behind the Brazilian was Michael Schumacher of Mercedes, who recovered well from Friday afternoon's crash but faces a 10-place grid penalty for causing a collision in the last race in Singapore.
Fifth and sixth fastest were the Sauber pair of Sergio Perez, the young Mexican who is bound for McLaren in 2013, and Kamui Kobayashi, the only Japanese driver in Formula one.
Seventh was France's Romain Grosjean in a Lotus, with Briton Jenson Button of McLaren eighth-quickest after being slowed by heavy traffic in a busy end to the one-hour session.
Paul di Resta also fought back well from a Friday accident to finish ninth fastest for Force India, whose other driver, Nico Hulkenberg, crashed heavily with 20 minutes of the session remaining.
Tenth fastest for Williams was Venezuelan Pastor Maldonado.