Sebastian Vettel's rivals have admitted defeat in the race for this year's title following the Red Bull driver's sixth win of the season in Valencia.

German Vettel extended his championship lead to 77 points after eight rounds with his lights-to-flag victory.

And despite there being 11 races left in the calendar, Lewis Hamilton said: "It's finished really. In the sense of the title it's almost over already."

"The championship is not in our calculations," added Fernando Alonso.

"If anyone thinks we can win the championship being eight-tenths of a second behind [Red Bull] they don't understand Formula 1."

Vettel and Red Bull have been almost completely dominant throughout the season.

The 23-year-old has secured pole position in seven of the eight races so far, going on to win six of them, and is the first man to finish first or second in the first eight races of a Formula 1 season.

In total, Vettel has dropped only 14 points all season, and his pace compared to his rivals in the last two races has been even more impressive given that the Canadian and European Grands Prix are not circuits ideally suited to the Red Bull's strengths - in particular on high-speed corners.

But the reigning champion refused to dwell on his championship lead after winning in Valencia.

"If you look at F1 compared to other sports it's a very long season," he said. "You will have some races where it will work and races when you will struggle and it will be difficult.

"I think you need to look at last year as an example. It shows that we [Red Bull] had good races up to a certain point and then things went wrong.

"Of course, our target is to be in the lead and make sure we stay there but the most important race to lead the championship is after the last one."

However, with the gap to McLaren driver Jenson Button and Red Bull team-mate Mark Webber now 77 points - McLaren's Hamilton is 89 points adrift and Ferrari's Alonso 99 points off the pace - Vettel's rivals all believe the race is only on for second.

Hamilton and Button are even concerned that the gap between them and Red Bull could be more pronounced in the next race at Silverstone.

"We've taken a step back this weekend - or maybe the others have gone forward," said Hamilton. "I think we're quite a bit down in downforce.

"We haven't made an upgrade on that for several weeks, especially rear downforce, and I think that in the next race we may really struggle again.

"I'm really not looking forward to Silverstone. Ferrari are a lot faster than us and the Red Bulls are on another planet."

Button added: "We need some really good upgrades going forward.

"We need to get our heads down and come up with something - particularly aerodynamically, I think. We need to take some risks.

"There's a big gap behind us to the Mercedes and a big gap in front of us in terms of Ferrari and Red Bull."

Alonso, meanwhile, reiterated his pre-race belief that his focus is solely on beating the chasing pack to second behind Vettel.

"I think second place is the maximum we can have in these days, so to be here between the Red Bull cars is a great achievement [today]," said the Spaniard.

"Our aim is to fight with the McLarens."

I don't buy this.

At this point last year, we were all saying that Webber had it sewn up and that Vettel made too many mistakes to win a World Championship.

Then after Spa it was Lewis Hamilton in the driver's seat and picked to go all the way.

Then it was Fernando Alonso going into the final race.

Then - low and behold - Vettel wins the World Championship.

Lots can still happen. I am not counting anyone out just yet.