Lewis Hamilton described Mercedes' new W09 as the "big sister" of its 2017 predecessor as he completed his first meaningful runs on Thursday.
Cold weather and rain on his first outing on Monday followed by the snow of Wednesday meant the Briton only really got the final afternoon to properly test the car he hopes can take him to a fifth Formula 1 championship.
That wouldn't hold him back, however, as he posted the fastest time of the week on the Medium compound tyres, three-tenths clear of Sebastian Vettel's best on Softs from Tuesday.
“I was really happy to get out, great to get on it,” Hamilton said after the session had ended. "So far it is positive. I’ve only had 60 laps but it definitely feels like a better car than last year.
“Driving a new car is like trying to crack a new code: you have to figure out which different techniques you need to get the most out of it, but the W09 feels like last year's big sister."
The defending world champion has insisted he would like a close fought battle with Red Bull and Ferrari this season, believing to come out on top would deliver the most satisfying type of success.
Sebastian Vettel has already made it clear Mercedes start the year as favourites, however, and now Renault driver Carlos Sainz admits the Silver Arrow looks very tough to beat.
"It's a little scary," he claimed, referring to the performance of the Mercedes engine.
"It's still early but it's also no secret that Hamilton and Ferrari will be fighting for pole in Australia. It's no surprise.
"I think it will be very difficult for teams like McLaren, Renault or even Red Bull to win because Mercedes and Ferrari are at a spectacular level."
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