Defending world champion Sebastian Vettel shrugged off technical problems as he dominated yesterday’s opening day of practice ahead of this weekend’s United States Grand Prix for his Red Bull team as he bids to clinch a third successive title.

Vettel, who was fastest in the morning free practice session ahead of Lewis Hamilton of McLaren, was quickest again in the afternoon ahead of his Red Bull team-mate Mark Webber as the champion team stamped their authority on the action.

The 25-year-old German clocked a best lap of one minute and 37.718 seconds to top the times in the second session to outpace Webber by seven-tenths of a second despite missing much of the afternoon running due to a water leak.

“It reduced the running time, but it was not too much of a worry,” he said. “And there is a day ahead for practice so I am sure we are ok. We are in the right place now.”

He added: “We got into the rhythm really quickly. This afternoon we had a bit of a problem and did not run as much as we would have liked to, but nevertheless we had two good runs – so we are well prepared for tomorrow.”

Although Vettel was fastest in both sessions, he said he believed the opening day’s action could end up being entirely irrelevant by time tomorrow arrives.

“On Friday, you need to be careful and the fact it is so slippery can make a big difference,” he said.

“I think there were one or two surprises today – and we will see what happens tomorrow. The track will constantly improve. It is important that we are among the guys at the top, and we’ll try and improve the car and go from there.”

Vettel’s only remaining title rival, two-time former champion Fernando Alonso of Ferrari, was third fastest ahead of Hamilton and his McLaren team-mate and fellow-Briton Jenson Button.

Alonso’s Ferrari team-mate Felipe Massa was sixth in the second session run on the ‘green’ new Circuit of the Americas.