US GP: Lewis Hamilton has 'gone up a level' as he closes on 2017 title

Mercedes boss Toto Wolff believes Lewis Hamilton has "gone up a level" after the championship leader enjoyed another perfect day at the United States GP.

Hamilton has won four of the last five Grands Prix and can even seal the 2017 drivers' title in Austin if results go his way, and he made the ideal start to the weekend by topping both practice sessions.

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The Englishman was half a second clear of main championship rival Sebastian Vettel in Practice One before out-pacing Max Verstappen in the next session.

"I feel he has gone up a level," Wolff said. "It's the fifth year we have worked together and both in and out of the car he has made a big step and it is very pleasing to see that."

A race victory, along with Vettel finishing sixth or lower, would seal Hamilton's place in motorsport history by becoming Britain's first four-time world champion and Sky F1's Pat Symonds agreed that he has never been driving better.

"His performance at the moment is just staggering," the F1 chief technical officer said. "If you look at second, third and fourth, you're seeing three guys close together but Lewis looks on a different plane.

"He's almost driving above himself at the moment."

'Rocket man' Lewis
Hamilton has been enjoying his time in the US before the Texas race, visiting the NASA Space Center in Houston earlier this week.

"I've got the red helmet today so I guess I was kind of a rocket man!" he joked to Sky Sports News' Craig Slater.

Along with Hamilton's recent Sunday form, his qualifying performances have also been impressive.

The 32-year-old has taken 10 poles this season compared to Vettel's three and he admitted that Fridays like he enjoyed at the Circuit of the Americas can only help his cause.

"Qualifying has been really good, but the Fridays have generally made the pace on Saturdays possible," Hamilton added. "So starting on the right foot often bodes well for the weekend."

More Vettel woes
But while Hamilton enjoyed a serene Friday, Vettel and Ferrari's recent malaise continued in Austin.

Vettel, who has dropped 56 points to Hamilton the last three races alone, finished half a second adrift of his rival in both sessions - and didn't complete a single race simulation lap in Practice Two.

He will now enter a crucial qualifying session with fresh reliability concerns after being stuck in the pits for the majority of the session with a suspension issue.

"It's Friday, you want to run as much as possible," he said. "That didn't work out for me today.

"Kimi [Raikkonen] was running in the other car so there's still a lot you can learn but we have to take it as it is right now and make sure that the car is in good shape tomorrow to get the rhythm and then I think we should be quick.

"It's important to feel comfortable. Obviously we're missing some laps but I'm sure with a couple of successive laps tomorrow it should be better.

"The car is quick so I'm not too worried."

Mercedes' technical chief James Allison conceded it was hard to conclusively analyse their performance while their main rivals have been struggling.

"We are also conscious that Ferrari had a bit of a troubled day today, so maybe we haven't yet really seen where the opposition are at," he said.

Will Lewis Hamilton clinch his fourth world championship in Austin? Watch the US GP weekend live on Sky Sports F1 - the race begins at 8pm on Sunday. Want to watch but not got Sky F1? Buy a NOW TV pass from £6.99!