Ross Brawn insists the title race is far from over despite Jenson Button extending his championship lead with just three races to go.

Button climbed up from 11th on the grid at the Singapore Grand Prix to finish fifth and gain a valuable point on team-mate and title rival Rubens Barrichello, leaving him 15 clear of the Brazilian.

Mathematically, only Sebastian Vettel can catch the Brawn GP pair but, 25 points behind with just 30 points remaining on offer, Vettel's chances look to have evaporated prior to Sunday's Japanese Grand Prix.

Brawn are also 42.5 points clear in the constructors' championship but their team boss refused to start any celebrations early.

“I've been to many world titles where I have lost them at the last race,” said a cautious Brawn. “So until it is done, it is not done.”

Brawn also insisted he would be doing Button no favours at the race in Suzuka despite the extent of the Briton's lead over his team-mate.

“This is as good as I've ever seen it in terms of two drivers trying to beat each other in a championship,” added Brawn. “They are very open and very honest with each other.

“And as for team orders, that just simply does not apply. I think the two drivers of the calibre we have got, you cannot separate one out unless it becomes mathematically impossible to win.”

Button was in celebratory mood following the night race in Singapore despite passing just one car — the Williams of Kazuki Nakajima — during the 61-lap race, which was won following a dominant drive by Lewis Hamilton.

Button said: “I had three title rivals and only one of them beat me and I've only lost a point. It has taken a lot of weight off my shoulders. It's like a victory to get these points — it was almost the perfect race for me.”

Under the medal system initially introduced by Bernie Ecclestone for this season, which was later scrapped following opposition from the teams, Button would have been crowned world champion in Singapore.

His six wins from the first race of the season would have been enough to outdo the next best of two victories, achieved by Hamilton, Barrichello and Vettel.

But Button said he was happy there was still a title fight going on. “I think points are the way to go in F1 even if the other way might have already worked in my favour,” said Button.

Hamilton, in what appears to be a dominant McLaren, is now the overwhelming favourite to win in Japan despite having never driven the circuit.

However he said: “I've heard that, apart from Monaco, it's the best circuit. I grew up watching it and I always wanted to go there.

“It's tough to learn and master a circuit in one weekend but we arrive there with momentum.”

Fernando Alonso, who boosted Renault following a tough week amid the Crashgate scandal with third place, is tipped to be unveiled as a Ferrari driver at Suzuka.

The two-time world champion, who dedicated his podium place in Singapore to his banned former team boss Flavio Briatore, is expected to be named as Kimi Raikkonen's replacement with the Finn tipped for a return to McLaren as Hamilton's team-mate.

It is anticipated that BMW Sauber driver Robert Kubica will then fill the vacant seat at Renault left by Alonso.