Michael Schumacher has said he expects a close fight for the world title after winning a battle with Juan Pablo Montoya in the Malaysian Grand Prix.
Schumacher said: "I think it's going to be a hard year, quite honestly.
"This is only the second of 18 races and we all know how quick development can be with some teams.
Schumacher said he was "really happy" with the progress made by tyre supplier Bridgestone, who have struggled in the Malaysian heat in the last two years.
"The difference we had compared to last year, specifically with our tyres - Bridgestone have done a superb job to compete in such extreme conditions," Schumacher said.
"I'm really happy with the way we fought our way back."
Montoya was encouraged by the performance of his Williams car, but refused to be too optimistic about mounting a season-long challenge to Ferrari.
The Colombian said: "The car needs a lot of work still. We don't want to be level with Ferrari, we want to be ahead of them.
"To be ahead we have to have a car that is consistent enough to win everywhere. They have the car to do that. We're close in places, but we still have to do a lot of work."
Ferrari technical director Ross Brawn said: "It was a great race. Being able to win here in some ways means more than Australia (where Ferrari dominated).
"Bridgestone have done a fantastic job when you realise how much we have struggled here in the past.
"It was a tough race. There were times when Montoya was pushing us and we couldn't respond, but luckily we were quick when we needed to be."