Vettel is emerging as Button's biggest potential title threat
By Mark Hughes
BBC F1 commentary box producer
Jenson Button's world championship bid could get a helping hand from an unlikely quarter - Ferrari.
With four victories from five rounds so far this year, a first world title is very much on the Englishman's horizon.
Surveying the speed of his rivals after securing pole position in Spain last weekend, Button noted with some concern just how much performance Ferrari had found as everyone introduced their traditional Barcelona aerodynamic upgrade packages.
"They've found way more lap time since the last race than anyone else," he said, "and we're obviously going to have to be watching them very carefully in the coming races."
Ferrari's new double diffuser and associated upgrades have found the car more than one second per lap of performance, enough to get it within 0.2secs of the Brawn and Red Bull at Barcelona, the most aerodynamically demanding of all the tracks.
Ferrai's improved pace could prove to be a benefit to Button
That bodes very well for the rest of Ferrari's season and is in stark contrast to the effectiveness of McLaren's twin-diffuser upgrade, which left the team trailing more than a second off the pace, limiting world champion Lewis Hamilton to a ninth-place finish.
But while Button was concerned about Ferrari's improved speed on Saturday, it may turn out to be a blessing in disguise for him.
After a troubled race in which he finished fifth, Massa was already conceding defeat in this year's championship.
"It's too late now for the championship," said the Brazilian, who lost last year's title by a point. "We just have to work on continuing to improve and try to win some races. But the championship, no way."
Had Massa been able to score a victory on Sunday, it was just about feasible he could still be a title contender. But now, 38 points behind with 11 rounds to go, his pessimism is understandable.
Nevertheless, the very fact that the Ferrari's development curve looks set to make it a potential race-winning car later in the season could well be what prevents Button's main rivals from being able to score as well as they would need to challenge Button's points lead.
Although team-mate Rubens Barrichello is mathematically Button's closest threat to the world title, realistically Button, on four victories from five and Barrichello on none, has now established himself as the team's number one.
Vettel spent virtually the entire Spanish GP held up by Massa's Ferrari
The real threat is Red Bull's Sebastian Vettel, who is in a car that Barcelona showed to be every bit as fast as the Brawn and is 18 points behind - not a devastating deficit with 11 rounds still to go.
It was only through starting on the less grippy side of the grid that Vettel ended up having his race ruined by being stuck behind Massa's Ferrari for almost the entire distance while the two Brawns escaped.
Vettel's pace in qualifying, considering his fuel load, was actually marginally better than Button's, while in the race the German's team-mate Mark Webber also showed Button-matching pace.
Brawn and Red Bull, two small, independent teams, are still the class of the field, albeit by a narrowing margin as Ferrari's superior budget and resource begins to kick in.
If Ferrari can maintain this rate of development - and their Barcelona car was just their first iteration of a twin-diffuser chassis; there is a lot more to come - then it would not be too surprising if they are setting poles and winning races in the near future.
Every time Ferrari do that, it is one less opportunity for Vettel to score the really big points he needs to eat into Button's lead.
So long as Button can keep scoring regular podium places, then Vettel has a much harder job on his hands than if his only rivals for victories were the Brawns.
Hitting the ground running as Button and Brawn have done could turn out to be absolutely the key to his future title success - in much the same way as Fernando Alonso managed to maintain early points cushions in 2005 and 2006 even as his key rivals developed cars faster than his Renault.
Mark Hughes has been an F1 journalist for 10 years and is an award-winning author of several books