Button shows Brawn's pace in Spain

The British driver's time of 1:19.127 put him a full second clear of his rivals, and was a similar margin faster than the best times of the previous two days.

Given the level of superiority, Button's lap was likely to have been set in low-fuel qualifying trim, but data from the rest of the test suggests that the Brawn-Mercedes has also been competitive on long runs and with heavy fuel.

Button had been fastest for much of Brawn GP's first public test on Monday, before being edged back to fourth place by the day's end, while his team-mate Rubens Barrichello took third place yesterday.

"It's been another great day and a very positive test generally," said Button.

"After the challenges we have faced, to come here and get off to such an encouraging start is just what we all needed and I can't thank the team enough. All that effort has really paid off and everyone can feel very proud."

Ross Brawn said yesterday that his car's performance was no surprise to him given the effort Honda had put into their 2009 programme before the parent company's exit.

"It's 15 months of work," he said. "We said that we were sacrificing last year to concentrate on this car, and what you see is what we said we would do. So it is perfectly rational in my mind."

Felipe Massa was second quickest for Ferrari today, having completed a grand prix weekend simulation. His programme was interrupted during the afternoon when a hydraulic problem left him stranded on track.

Robert Kubica (BMW Sauber), Timo Glock (Toyota) and Renault's Fernando Alonso completed the top five, with Sebastian Vettel sixth for Red Bull despite ending the day in the gravel at Turn 4.

McLaren's apparent difficulties continued as Lewis Hamilton brought up the rear of the 10-car field, 2.5 seconds slower than Button. The world champion also had a brush with the tyre barrier, causing minor damage to the front of his car, after going off on the exit of Turn 2.

Today's times:

Pos  Driver        Team                      Time      Laps
 1.  Button        Brawn-Mercedes       (B)  1:19.127  124
 2.  Massa         Ferrari              (B)  1:20.168  109
 3.  Kubica        BMW Sauber           (B)  1:20.217  109
 4.  Glock         Toyota TF109         (B)  1:20.410   99
 5.  Alonso        Renault R29          (B)  1:20.863  107
 6.  Vettel        Red Bull-Renault     (B)  1:21.165  102
 7.  Rosberg       Williams-Toyota      (B)  1:21.324   89
 8.  Fisichella    Force India-Mercedes (B)  1:21.545   97
 9.  Buemi         Toro Rosso-Ferrari   (B)  1:21.569  140
10.  Hamilton      McLaren-Mercedes     (B)  1:21.657   82

All Timing Unofficial