Mark Webber's Red Bull ground to a halt during the final quarter of the afternoon practice session at Monza.

Mark Webber's Red Bull ground to a halt during the final quarter of the afternoon practice session at Monza.

The championship contender pulled off the track with a water pressure problem that should be easily fixed, a representative of the Austrian-owned team said.

His teammate Sebastian Vettel fared better, adding a P1 to his competitive time set in the earlier morning session.

And the Ferraris were also on the pace in the afternoon, ahead of Lewis Hamilton's McLaren, who was running an F-duct-free MP4-25 in order to compare it with the downforce-stalling configuration on teammate Jenson Button's car.

With the F-duct, Button was mere hundredths slower than Hamilton in the afternoon.

"Our car works very well in low downforce," said Button. "We should be fighting at the front."