Australian GP: Phenomenal field out to stop Vettel at the start

World champion Sebastian Vettel is understandably favourite to open the Formula One season with a victory at the Australian Grand Prix this weekend but there are strong indications he will face a much tougher challenge than he did last year.

The German's pole-to-flag victory by a formidable 22.2 seconds at Albert Park last year started a second season of dominance for Vettel and his Red Bull team that culminated in the retention of drivers' and constructors' championships.

The return to the grid of Kimi Raikkonen after a two-year sabbatical, however, has resulted in the tantalising prospect of five former World champions, not to mention a string of young pretenders, fighting to deny Vettel a title hat-trick.

"This season looks like a stellar year for Formula One with six world champions. It's unprecedented," Red Bull team boss Christian Horner said.

"The quality of the field is phenomenal. I think it's going to be a really exciting season. We're obviously determined to try and carry the momentum we've gathered over the last couple of years into this season, but we certainly don't take anything for granted."

Despite the millions of dollars invested in building the cars and the thousands of kilometres run in testing, no one really knows how the contenders will match up until the covers come off the tyres for Saturday's qualifying session

Indications are, however, that McLaren, who boast two of the former World champions in Britons Lewis Hamilton and Jenson Button, will be more competitive from the off than they were after a difficult winter last year. They have pedigree on the Melbourne street circuit too.

Button, runner-up in the title race last year, won back-to-back in Melbourne in 2009 and 2010 with Hamilton winning in 2008. "I actually feel more relaxed and ready for the new season than I think I've ever done," said Hamilton, who was fifth in the championship last year."

"Everything has gone smoothly with the car -- which is more than we can say for last year -- and it just seems to be a responsive and reliable package."

Raikkonen won in Melbourne in 2007 on his way to winning the title for Ferrari and looks to have eased seamlessly back into Formula One with Lotus, who ran as Renault up until last season.

The 32-year-old Finn left the sport after battling with his motivation and, from what he showed in testing, would seem to have a car which could offer him the chance to fight for podiums at least.

Ferrari's former World champion Fernando Alonso, the 2006 winner in Australia, never needs any motivation but he and his team-mate Felipe Massa look like facing an uphill battle to get on the podium in their radically overhauled 2012 car. Seven-time World champion Michael Schumacher won the last of his four Australian Grand Prix in 2004 and his Mercedes team are another who have great hopes after positive winter tests.

One contender who has never won a World title, nor a Grand Prix at Albert Park, is Vettel's Red Bull team-mate Mark Webber and the Australian will be at least hoping to improve on his best finish of fifth in his home race.

"This will be my eleventh Australian GP and I can't wait to get started," said the 35-year-old, who finished third in the championship last year.