BAR's Jenson Button turned the heat on Michael Schumacher as Ferrari's world champion geared up to equal Formula One's best start to a season at the Spanish Grand Prix.
Schumacher, chasing his fifth win in a row on Sunday to equal Nigel Mansell's 1992 record run for Williams, finished the day with the fastest time at the Circuit de Catalunya.
But it was his young British rival who stood out after blitzing the field in the afternoon's second session to increase his hopes of a fourth podium in a row.
Schumacher's best time of 1:15.658 seconds in the first session was more than two seconds quicker than his 2003 pole position performance at the Circuit de Catalunya.
Button was the only other driver to lap in under one minute 16 seconds and his time of 1:15.935 came in an afternoon punctuated by occasional light rain.
Schumacher's Brazilian team mate Rubens Barrichello was second quickest in the morning but Button and BAR team mate Anthony Davidson, the test driver who will not race on Sunday, dominated the second stint.
Schumacher has won the last three Spanish grands prix and is the overwhelming favourite to win again on Sunday in what will be his 200th grand prix.
But he has cast wary glances at on-form Button, who started the last San Marino Grand Prix on pole position and finished second.
Local favourite Fernando Alonso, second in front of his home crowd last year, was seventh quickest for Renault in the morning and fifth in the afternoon.