Alonso singles out Button threat

"He never makes mistakes and competes in all circumstances," Alonso told reporters on Friday.

The Spaniard completed 14 laps during the two practice sessions at the Albert Park circuit and only Button of the drivers racing on Sunday clocked a faster time.

Button was fourth fastest in Friday's two sessions, more than two tenths of a second faster than the Renault of Alonso, but behind the pace-setting trio of test drivers Anthony Davidson, Alexander Wurz and Robert Kubica.

Alonso spectacularly usurped Button as the most promising driver in the paddock when he became the youngest world champion in the sport's history last season at the age of 24.

But Alonso believes Button, who is still win-less since making his debut for Williams at Melbourne in 2000 at the tender age of 20, will need all factors to be right to fight for the title.

"I think he can do really well and the car is now very competitive. We all saw him in 2004 when he was third behind the two Ferraris, lots of podiums and that showed he has to be a consistent driver.

"But to be the world champion you need something more. You need to win races and be lucky.

"You need to be strong in the important parts of the championship and you need a team that is always developing."

Renault's famed superior starting speed remained, Alonso maintained, but he believes the improved Button would be a difficult prospect to overtake if the Briton can translate his practice form into a front-row grid slot in Saturday's qualifying session.

"Honda are similar to us, close to us. We are the best starters in the paddock still but they have improved a lot from last year.

"It's not nice to have Button in front of you because the Honda is starting very well. It will be difficult if Button is in front of me, it will be very interesting."