LEWIS Hamilton s defence of his F1 world title got off to a disappointing start in Melbourne earlier today (Friday). The 24-year-old reigning champion from Tewin was well off the pace in practice for Sunday s Australian Grand Prix. Vodafone McLaren Merced

LEWIS Hamilton's defence of his F1 world title got off to a disappointing start in Melbourne earlier today (Friday).

The 24-year-old reigning champion from Tewin was well off the pace in practice for Sunday's Australian Grand Prix.

Vodafone McLaren Mercedes star Hamilton was only 16th fastest out of 20 in the first session around the Albert Park circuit - more than two seconds slower than the quickest driver.

He was then third slowest in Friday's second session in Melbourne as Nico Rosberg dominated for Williams.

Rosberg set the pace in both sessions with Brawn GP's Rubens Barrichello clocking the second best lap time of the day.

Unless McLaren can find a dramatic improvement in their car, world champion Hamilton - winner in Australia last year - will start Sunday's opening race of the grand prix season from the back of the grid.