SEPANG  - Defending world champion Sebastian Vettel finds himself in the unaccustomed position of playing catch-up as what is shaping as a gripping Formula One season hits steamy Malaysia this week.

Red Bull's precocious young German was never headed last year as he swept to his second straight title, and he has led the standings since November 2010, when he coolly won a last-race showdown for his maiden championship. But the 24-year-old from Heppenheim knows he has a fight on his hands for only the third hat-trick in Formula One history, after McLaren emerged from pre-season testing to dominate the year's opening grand prix in Australia.

Former champion Jenson Button won in impressive style and Vettel had a timely safety car intervention to thank as he nipped in front of McLaren's Lewis Hamilton to finish second. Red Bull's Mark Webber was fourth. Now Red Bull and McLaren, who have not won the drivers' title since 2008, are already locked in a tussle to get the most of their cars and drivers as they size up the Malaysian Grand Prix, one of the year's toughest races.

"We saw it last year where there were swings and roundabouts -- with some circuits suiting different cars and different characteristics," Red Bull team principal Christian Horner told "So I think there are circuits that will affect performance, but I think the teams are very closely matched at this point of time," he added.

"As always, though, it will be a development race between now and the end of the season. Whoever gets the most performance from the car quick enough will see a gain from that." Easy-going Vettel was typically nonchalant about the McLaren challenge, even after Button joked that he hoped he'd seen the last of the German's famous crooked-finger celebration.

"We will see what we get next weekend," Vettel said. "If I remember last year, we were pretty dominant (in Australia) and then qualifying was just a couple of hundredths between Lewis and myself, so we will see what happens." Red Bull are assumed to have been hit hardest by a ban on blown diffusers, a system they pioneered which channels exhaust fumes to increase downforce, while both teams were taken aback by Mercedes' new drag-reducing rear wing.

But gearbox problems forced Mercedes' seven-time champion Michael Schumacher out early in Australia, and team-mate Nico Rosberg finished 12th. Meanwhile Ferrari, by common consensus, were flattered by Fernando Alonso's determined drive to fifth in the unloved F2012, which stumbled in testing and has been criticised as appearing over-innovative.

All teams are facing one of the year's biggest challenges at tropical Sepang, where brutal heat and humidity -- frequently punctuated by torrential downpours -- make for a demanding weekend. "It is one of the most physical circuits of the season," said Sauber's Sergio Perez. "The heat is demanding for the drivers and also in terms of tyre degradation. It is not an easy circuit to race on, and it is quite technical."

Formula One's finances are also in the spotlight after reports that officials are considering a share-market flotation as part of negotiations for a new Concorde Agreement governing how profits are shared. Free practice starts on Friday with the race, over 56 laps of the 5.5-kilometre (3.4 miles) Sepang circuit near Kuala Lumpur, starting at 4:00 pm (0800 GMT) on Sunday.