Lewis Hamilton 'in league of his own' in Australia practice, says Toto Wolff

Toto Wolff says Lewis Hamilton is "in a league of his own" after the Mercedes driver dominated both Friday practice sessions for the Australian GP.

After a tight winter testing, the world champions showed they are once again the team to beat in 2017 with Hamilton over half a second clear of the rest of the field in both P1 and P2.

Hamilton's lap of 1:23.620 in the second session was within one tenth of the quickest lap ever recorded at Albert Park.

While Sebastian Vettel's Ferrari split the two Mercedes in the afternoon, the Brit comprehensively outpaced new team-mate Valtteri Bottas in both outings, and Wolff believes no one can currently match the three-time world champion.

"Hamilton is in a league of his own at the moment," Wolff told Sky F1.

"His one-lap pace was really good and he took the ultrasofts for 17 laps and was stable. I'm happy."

Hamilton had played down Mercedes' chances on Thursday after winter testing and suggested Ferrari may be quicker than the Silver Arrows.

But he admitted Mercedes had made "night and day" improvements from the second test in Barcelona, although he remained cautious ahead of Saturday's qualifying.

"It was a night and day difference to how the car felt in the last few days of testing so that was a big relief for all of us.

"It was 99 per cent perfect," Hamilton said. "After struggling with some issues in Barcelona, we didn't know if we'd have the same thing here. What's really encouraging is that we've arrived at the track just a week later and the car is exactly where it should be.

"It's feeling great out there and the guys have done a fantastic job. We've shown good form so far on both the long and short runs and we got every lap done that we wanted to.

"Coming into today, we really didn't know where we'd be. We knew from FP1 that the Ferraris weren't at their maximum. Of course, in P2 all of a sudden they were quick. We'll see tomorrow how it really stands."

Hamilton's best time on the ultrasoft tyre was also over a second clear of Daniel Ricciardo and Max Verstappen's Red Bulls - the heavily revised RB13 car struggling for performance on Pirelli's fastest compound.

However, 12 months ago Hamilton was fastest in all three practice sessions and secured pole position before a poor start cost him the chance of the race win.

Red Bull boss Christian Horner acknowledged Hamilton is the man to beat but believes there could be more unpredictability on Sunday.

"From the performance we've seen today from Lewis, he's the absolute favourite," Horner said.

"He was the favourite coming here and all today has done is underline that.

"But then it's motor racing, and anything can happen. We have seen spurious results in opening Grands Prix in previous years."

In contrast to Hamilton, Bottas endured a challenging day in his first official sessions with Mercedes since replacing retired world champion Nico Rosberg.

The Finn was unable to get close to his team-mate and admitted there was more to come from him as he continues to adapt to his new car.

Bottas said: "Overall it was a good day today. We still have work to do with the car balance but we got all of our running completed without any issues.

"From my side I definitely feel like I can make a step forward tomorrow. It'll be a busy evening for us tonight looking through all the data to see where we can improve but it's a reasonable start. In terms of our pace, it is only practice, so tomorrow we'll find out exactly where we are."

Wolff backed Bottas to close the gap at the front, saying: "I'm very confident he's going to find the pace and earn his place in the team."