Ferrari were faster this year in pre-season testing and a strong start for them will test arch-rivals Mercedes.
"Judging from the performance in Barcelona, it looks like we will have a proper fight on our hands," Mercedes team principal Toto Wolff said to BBC.
"But an F1 season is not just about who comes out of the blocks quickest," he added.
'This is going to be the toughest battle yet'
"This is going to be the toughest battle yet. We've got the best team around us. We have experience, it's no coincidence that we are world champions so we have to be diligent and stay balanced," said Hamilton, who has won twice in Melbourne.
Here's how the two sides will line-up
Last season Hamilton dominated the show after bagging 11 of the final 19 races.