A supremely-confident Sebastian Vettel topped the times with ease ahead of his Red Bull teammate Mark Webber in Friday’s second free practice session for this weekend’s United States Grand Prix.

After a frustrating morning session curtailed by fog and an errant medical helicopter, during which he was only 18th fastest, the newly-crowned four-time world champion blasted back to lead the way.

He clocked a best lap in one minute and 37.305 seconds to finish one-tenth of a second ahead of his retirement-bound team-mate who later suggested that the champion may have been toying with his rivals.

Webber, who would dearly love to end Vettel’s triumphant run, said he felt the 26-year-old German did not really show his true pace.

“Seb did a pretty good lap – at his fourth attempt,” said Webber. “So I don’t think he got the best out of his tyres, unfortunately. Or, fortunately for him, but unfortunately for us.”

Webber reminded reporters of the way in which Vettel had made a dramatic step on race day in Abu Dhabi two weeks ago.

He added that little should be read into his practice form.

“I will try and get involved again if I can tomorrow,” he said, recalling that he was able to grab pole position at the Yas Marina circuit, a feat that provoked Vettel’s sharp response.

“He wasn’t too happy in Abu Dhabi, but then he destroyed us in the race. So I will try to have a clean Saturday and Sunday and get the best result for myself and the team.”

It was a dominant performance again from Vettel who is seeking his eighth consecutive victory of the season in Sunday’s race at the Circuit of the Americas in Austin, Texas.

The Mercedes pair of Nico Rosberg and Lewis Hamilton were fourth and fifth fastest ahead of Heikki Kovalainen, who made an impressive return as replacement for compatriot Kimi Raikkonen at Lotus.

Hamilton, who admitted he has been suffering poor form since the European summer break, looked faster and sharper and was hopeful his new Mercedes chassis will solve his recent problems.

The 2008 world champion has a new chassis because the team found what Hamilton described as a hole in the car he had used during the Abu Dhabi Grand Prix.

“On the long runs, it did feel better so I’m hoping that when the car is heavy with fuel in it, I would like to think it will be as good as it is now,” said Hamilton.

“So fingers crossed, it will be better this weekend.”

As Raikkonen underwent successful back surgery in Strasbourg, Kovalainen confirmed his potential with an excellent showing to wind up ahead of sixth-placed Esteban Gutierrez and his Sauber team-mate Nico Hulkenberg.

Kovalainen’s Lotus team-mate Romain Grosjean was eighth ahead of Jenson Button of McLaren and two-time champion Fernando Alonso of Ferrari.