Former F1 World Champion Jenson Button has warned McLaren-Mercedes' rivals that the significant leap forward in performance made by the hitherto troubled MP4-26 in the Australian Grand Prix in Melbourne just under a fortnight ago was merely 'the first step' for the team - as he forecasts 'a very different race' this weekend at Sepang.

With McLaren's new baby having been all out-of-sorts in terms of both reliability and raw pace during pre-season testing, some 'dramatic changes' between the final test and the F1 2011 curtain-raiser around the streets of Albert Park enabled Lewis Hamilton to both qualify and finish second to Sebastian Vettel in the runaway Red Bull Racing - and Button could arguably have backed his team-mate and compatriot up in third place in the grand prix had it not been for his drive-through penalty for going off the circuit when overtaking Ferrari rival Felipe Massa.

As the F1 2011 circus readies itself for seconds-out, round two with the Malaysian Grand Prix, however, the British star - who achieved pole position and race victory in Kuala Lumpur as he sped to the drivers' crown two years ago - is adamant nothing can be taken for granted.

"We don't know what other people have been doing over the last two weeks, what they are bringing to this race," he insisted, "but already in Australia, I think we should be happy with the performance that we had compared to what we had in testing. It was the first step really with the package that we had.

"We have some upgrades here to sort of fine-tune the package, which will give us more lap time and hopefully better consistency - but whether it's enough to challenge the Red Bulls, I don't know. There's a lot more that will come into play here, I think, in terms of the tyres. I think it will be a very different race to what we saw in Melbourne."

Ah yes, the tyres. Pirelli's rubber was one of the main talking-points in the days after the Australian Grand Prix, but not for the reasons that might have been anticipated. Far from decrying the tyres - and the super-soft compound in particular - as not durable enough as had been the case all throughout the winter, drivers were if anything bemoaning them for being too durable Down Under. Again, however, Button warns that the sheer heat and humidity of Malaysia will likely reveal a different picture and provide an altogether sterner challenger - and for the drivers, too.

"It is very hot here," the 31-year-old reflected of what is by common consent the toughest race of the season from a physical point-of-view. "However much training you do, you still can't get away from the humidity. It is tough, and it's very difficult to simulate driving in humidity because it is very, very physical and it takes it out of you - and you can get quite claustrophobic. I have done a bit of training over the last weekend; I was in Hawaii for the week which was good, getting used to the humidity and pushing myself in the hot conditions.

"It's a very tough circuit for the cars, for the drivers but especially for the four things that are touching the road in the hot temperatures. I think there will possibly be more degradation. I think we were all surprised at how consistent the tyres were in the first race.

"I don't think that was the initial idea with the Pirelli tyres, to be so consistent. We saw a one-stop from [Sergio] P?rez, which was obviously the highlight of the race for a lot of people with how he was able to be so consistent, but I don't think it's going to be the same here. I think it will be very different - it's a lot more demanding and a lot tougher on the tyres. It brings another element into it."

Praising the Malaysian fans for their warm welcome and support, Button admitted that Sepang is a circuit that 'really makes me smile', describing it as a very 'flowing' 5.5km layout that has been 'designed very well in terms of overtaking', making for 'fun racing'. What's more, the potential of the new moveable rear wing - or Drag Reduction System (DRS) - should be more immediately obvious than it was at Albert Park, he suggests.

"Even with the DRS, it is still very tricky to overtake at a place like Melbourne with such short straights," he explained. "If you cover the inside line, it is very difficult to overtake. At Sepang, I think the DRS system is going to make overtaking a lot easier than it was in Melbourne - it is one of those circuits where you can really have a good tussle, as corners flow into each other. Maybe it will be a little too easy, as I think being within a second before the last corner, even without DRS, you can have a good chance of overtaking. I don't know, we'll see."

The greatest variable of all in Kuala Lumpur, of course, is the weather, with thunderstorms forecast at some stage for all three days of the grand prix weekend. Two years ago, the race had to be stopped early due to the sheer amount of standing water on the track and the rapidly fading light given the late-afternoon start, and last year, McLaren got things very wrong in qualifying by failing to accurately read the elements, a mistake that Button vows 'we won't be making again'.

"We've got to be prepared," he asserted, "and I think we will be. The weather can really play a big part here; there's a big chance of showers and thunderstorms, which makes it tricky for every team in the pit-lane and for every driver to really understand the conditions and make the right call.

"When it does rain over the circuit, it's very, very heavy rain. You get to four or five in the afternoon and it just pours it down! I remember back in 2009 when I was racing for the world championship, I was driving around in the lead of the race and it just chucked it down. It was up to the front wing of the car; there was so much water, the car was just floating. Luckily enough, they did stop the race - they red-flagged it because it was too dangerous.

"Last year, again, we had some very tricky conditions in qualifying and I ended up in a gravel trap, which was a pity, because it hurt my end result. It's always very mixed over the race weekend - you're never really sure which direction it's going to go - so when you go to Malaysia, you've really got to think about the different conditions and be ready for anything."

That being the case, strategy, he concedes, will be vital, but still, he acknowledges that McLaren will be up against it in its efforts to turn the tables on Red Bull in Malaysia, where car aerodynamics - an RB7 fort? - are widely-anticipated to come into their own.

The chief ace up the Woking-based outfit's sleeve is its proven KERS system, with its rival yet to decide whether or not to run the performance-enhancing, energy-saving technology at Sepang, having elected against it ostensibly on reliability grounds in Melbourne. Vettel has estimated its advantage to be as great as half-a-second per lap, whilst team-mate Mark Webber reckons it is a 'no-brainer' to use it this weekend.

"We lose more than a little bit of time if we don't use KERS," Button revealed, having already expressed his opinion that RBR's 'reliability' excuse Down Under was little more than a smokescreen to disguise the fact that the defending double F1 World Champions are struggling with their own device. "I think we have a very good system; I don't know what Red Bull's system is like.

"Everybody has a different KERS hybrid system in F1, so maybe it gives them a lot of time, maybe it doesn't, I don't know. I don't know what the benefits are for them. And then there's always reliability issues, aren't there, with a new system? I'm sure that's one of the reasons why they didn't use it in Melbourne, and I'm sure they're weighing up whether it's worth it or not [in Malaysia].

"We need a powerful KERS to compete against them, because in every other area they are very competitive. At the moment, I think we're a long way from Red Bull. I get the impression that Seb [Vettel] is yet to show the full potential of that car."