Jenson Button fears the prospect of first-corner "mayhem" should Felipe Massa get a flyer in his Ferrari at the start of tomorrow's Spanish Grand Prix.

Button produced a stunning one-lap performance in qualifying today to claim the sixth pole of his career, and third this season with Brawn GP.

The world championship leader crossed the line to start his final hot lap with just two seconds to spare of the 10-minute period, and 80 enthralling seconds later he had deposed Sebastian Vettel from top spot.

Underlining the critical nature of his latest pole, the last eight winners - and 13 of the previous 14 overall at Barcelona's Circuit de Catalunya - have started from top spot on the grid.

But this year, in comparison to those past races, there is KERS, the device that gives a select number of cars at the moment a short burst of power at the touch of a button.

None of the top three in Button, Red Bull's Vettel and Rubens Barrichello possess KERS, but fourth-on-the-grid Massa does, and he threatens to be the unknown quantity.

As Button remarked: "I've heard that KERS gives you 10 metres from the start to the first corner, which is quite a lot, so that's a problem.

"If he (Massa) gets a good start it could be a problem for me, but I think it will make it a bit crazy going into turn one more than anything else.

"When one car is going into the first corner a lot quicker than those in front of him, it could cause mayhem, especially at quite a high-speed corner like this one.

"So it will be about keeping your nose clean going into turn one, and that's going to be difficult for all of us."

Ferrari's improvement in form this weekend has been startling as Massa at least proved as another mistake in qualifying cost Kimi Raikkonen dear, with the Finn starting 16th.

Massa, who stands on the brink of ending his worst start to a F1 season after failing to score a point in the opening four races, is grateful for the advantage he could have tomorrow.

But the Brazilian knows he cannot afford to become embroiled in any early carnage if he is to have a hope of breaking his duck.

"Overtaking three cars is not so easy," assessed Massa of the task he faces when the five red lights disappear.

"I'm very happy to have the KERS at the start tomorrow, and I'm in a reasonable position, but I'm on the dirty side.

"Let's see what happens, see how good our car can start compared to the others.

"But the most important thing is to think about the race. I think we can have reasonably good pace, and that is good motivation for the race."

Additional motivation for Button is that for the first time since last year's British Grand Prix, mum Simone is at this race, and it gave him great pleasure to claim pole with her watching live.

"I'm very happy, not only because this was unexpected, but my mum is here at this race, and I'm glad she's here to see me get pole," added Button.

The question now is whether he can convert that position into a fourth race win in five grands prix, and extend his current 12-point lead in the championship.

"I know pole is important because it's difficult to overtake here," remarked Button on the Barcelona track.

"P1 is an advantage. I just have to hope I can stay there into turn one.

"But as you know we (he and Barrichello) have both have had some difficulties with starts.

"Those we have made have been very good, and I hope we can have one of those starts tomorrow.

"But I have to say that was by far the best lap I've had this weekend, so I'm very happy.

"When I heard the shouts I had qualified on pole, it felt very good.

"The package we have here is a good step forward. We just have to work with it a bit more and get the most out of it - I hope we can anyway.

"But I'm excited. I didn't expect to be sat in this position at the moment."

What Lewis Hamilton would give to be in that position again as the expected woeful weekend for McLaren is coming to fruition.

The world champion will start from 14th, the worst position of his F1 career in the dry, whilst team-mate Heikki Kovalainen is down in 18th, his lowest grid slot since joining the team.