He outpaced nearest rival Kimi Raikkonen of Ferrari by two-hundredths of a second in a dramatic conclusion to a keenly fought session.

Button's Brawn teammate Brazilian Rubens Barrichello was third ahead of Sebastian Vettel in a Red Bull and Felipe Massa in the second Ferrari.

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German Nico Rosberg was sixth for Williams and Finn Heikki Kovalainen seventh for McLaren Mercedes ahead of Australian Mark Webber, in the second Red Bull, two-time champion Fernando Alonso of Renault and Japan's Kazuki Nakajima in the second Williams.

"I think Jenson is getting into the habit of saving the best for last," said Brawn team chief Ross Brawn.

"He knew that was the lap where he had to produce it and he's just driving exceptionally well at the moment."