Sauber overcame a lengthy delay to the start of practice at the United States Grand Prix to put both its drivers into the top seven on the timesheets.

Friday morning practice started over half an hour late due to poor visibility, and was then interrupted because of a technical problem with the medical helicopter. This resulted in the session being reduced to 45 instead of the usual 90 minutes, but Sauber was still able to put circuit rookie Esteban Gutierrez into fourth overall, with Nico Hulkenberg ninth.

The afternoon went more according to plan, with Guti?rrez and H?lkenberg able to work through their respective programmes without any technical difficulties. However, while the performance was good - the pair finished sixth and seventh respectively - both drivers still see more room for improvement.

"Overall, this was a very positive day for our team," head of track engineering Tom McCullough confirmed, "FP1 was cut short due to the fog and helicopter problems, but that was the same for everybody, and we prioritised on the long-run, high fuel pace this afternoon in order to understand how the tyres perform on this track, which is much cleaner compared to last year.

"It was a new track for Esteban, but he got on top of it quickly, doing a solid job today. Our performance on both low and high fuel is reasonable, but there is still more we can get out of the package, so we are working hard to do that tonight."

Guti?rrez, who only had a watching brief as the regular Sauber drivers got the maximum track time a year ago, shrugged off the delayed start and remains hopeful of a good result at the closest thing to a 'home' race.

"It was a very productive day," he reported, "Although the delay wasn't ideal, I feel comfortable with the track and enjoy driving here, which is important.

"We are in a good shape, but now we need to focus on maintaining it for qualifying tomorrow and the race on Sunday. I think we have very good chances for a good result here. There are two more races to go and my goal is to get the maximum out of what we have."

H?lkenberg, whose future remains uncertain while he waits to hear whether Lotus will be picking up his services for 2014, agreed that it had been a good day.

"This morning was a bit of a funny situation with the fog delaying FP1 but, once the session started, everything went well and we managed to get through the programme we had planned," the German commented, "The car was okay and the performance is looking good too. However, I think there is still room for improvement, as I'm not happy with the balance on the medium tyres yet. It will be tight tomorrow, but I think we can improve."