Webber's time of 1:22.693s was set towards the end of the day when the circuit was at its driest and marks the first time Red Bull has ended the day quickest in 2013.
Lewis Hamilton topped a wet morning session and ended the day in second place, almost two seconds shy of the Australian. The 2008 world champion completed the most laps, circulating 113 times.
Jean-Eric Vergne was third, ahead of Williams rookie Valtteri Bottas and Mexican duo Sergio Perez and Esteban Gutierrez.
Gutierrez caused one of the day's three red flags when he skated off the damp circuit at Turn 3. Lotus's Romain Grosjean also spun off during the wet weather at Turn 12.
The final stoppage of the day was caused when Felipe Massa's Ferrari stopped on the exit of Turn 9.
|1||Mark Webber||Red Bull||1:22.693||90|
|3||Jean Eric Vergne||Toro Rosso||1:25.017||59|
|7||Paul di Resta||Force India||1:27.107||57|