'We had our weaknesses last year here and there and we obviously try to fix those and do much better this year.
For sure it's a new challenge for the whole team.
"This is going to be the toughest battle yet", said the Briton, although Mercedes, who have won five drivers' and constructors' titles in a row, may not have shown their full hand yet.
"We are definitely in the fight and we know we have a strong team".
"But as a driver for sure I have to figure out how can I pull more out, which I don't have the current answer for".
Hamilton will be looking to draw first blood in his battle against the Ferraris of Vettel and Leclerc in Australia, but could his Mercedes teammate Valtteri Bottas emerge from a torrid - and winless - 2018 and put the pressure on the reigning champion?
It was the four-time world champion's second straight win in Melbourne and he followed it up with victory at Bahrain before a resurgent and doggedly consistent Hamilton won 11 of the final 19 races to leave the frustrated German in his wake. "This year we are more prepared, our vehicle seems to work fine".
Despite its slump in the second half of previous year that cost Ferrari clinching both championships, Vettel believes it has every reason to be confident it will address its 2018 weaknesses and begin this season in a much stronger position.
The bookmakers have Vettel as clear favourite to win on Sunday although new Ferrari team chief Mattia Binotto suggested Mercedes were not as far off the pace as Hamilton suggested.
"I think I've learned to take things a bit more relaxed and once you learn a bit more about yourself you tend to find those things that you want to do that you feel are best for you in terms of preparation, whether it's hanging out with friends, whether it's being 24/7 at the gym, finding the balance in your free time and fun stuff, work stuff, finding that balance, I've been able to fine tune it a bit and in general feel more relaxed about everything".
Max Verstappen, who at 17 was the youngest driver ever to start a race, is now a 21-year-old "veteran" in his fifth season and the main man at Red Bull, who also have 23-year-old Frenchman Pierre Gasly racing for them.
Three drivers make their race debuts in Australia - Lando Norris (McLaren), Alexander Albon (Toro Rosso) and George Russell (Williams). 'So far, the spirit is right, the team is on track, the auto feels good so let's see how we start the year.' Hamilton, meanwhile, is braced for a scrap. A victor now gets 25 points with 18, 15, 12, 10, 8, 6, 4, 2 and one for the subsequent places.
The new regulations have changed the front and rear wings, aimed at making it easier for cars to get closer and overtake.