Mercedes finished Friday practice in third and fourth positions on the timesheet at the Circuit of the Americas, leaving Nico Rosberg optimistic that it can challenge Red Bull on raceday.

Although team-mate Lewis Hamilton admitted that he was still wrestling with the W04's balance, both drivers completed more than a full race distance during the day, working on set-up and tyre evaluation.

"This afternoon, we had a very good session," Rosberg confirmed, "The car felt like it was on rails and I was very happy with the balance. I hope we can give the Red Bulls something to think about this weekend and I will be pushing 100 per cent for another podium.

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"It's really difficult to get it right with the tyres here as the track surface is very smooth and the compounds are very hard. Therefore the tyres are lasting a long time and a lot of people will try to manage only one stop on Sunday."

In contrast to the German, Hamilton admitted that he was still struggling to pin down the set-up of his car, which is all-new after cracks were found in the chassis he had used in Abu Dhabi, and completed a single long run on option tyres in the afternoon session while Rosberg ran the hard compound 'prime' then the medium 'option' for his high-fuel runs.

"The circuit was quite green today, which made it pretty slippery out there as we are using the two hardest tyre compounds this weekend," the Briton, who had several off-track moments, confirmed, "After we changed the chassis yesterday, the car felt better to drive, particularly on the long run when it was pretty consistent, so that's a positive for me.

"The option tyre is working well for a long stint, which may open up some possibilities for us with race strategy. It was a pretty straightforward day although we still have some work to do to nail the set-up because it's not quite there yet. But we're all focused on ending the season on a high and taking that foundation with us into the winter."

With the W04 'best of the rest' on the timesheet behind the Red Bulls, technical director Ross Brawn confirmed that the day's changing weather had been the major concern.

"It was a fairly straightforward and trouble-free day of running, once we finally got underway after the fog cleared!" he noted, "The track and tyres seemed pretty consistent; the biggest problems came from the gusting wind which was causing a few problems. Overall, the car seems to be in reasonable shape. We completed our programme and particularly the important high-fuel running, and things looked pretty sensible all round."