Jenson Button insists that he has reasons to be positive about the United States Grand Prix, despite being handed a grid penalty after the opening practice session.

The Briton posted the second fastest time of a delayed and truncated Friday morning practice, but was later slapped with a three-place penalty after passing rookie Daniil Kvyat under red flags as the session was stopped to summon a replacement medical helicopter. The cars had only just been released after a lengthy delay to wait for heavy fog to clear over the Circuit of the Americas, and Button held his hand up to the 'error'.

"It wasn't a dangerous situation, and I didn't do it on purpose - the other car slowed down - but the rules are the rules, and it was the wrong thing to do," he conceded, having passed Kvyat on the long backstretch of the Austin venue.

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Although he slipped to ninth on the overall order after second practice, less than a second off Sebastian Vettel's ultimate pace, the 2009 world champion insisted that both sessions had been encouraging for the McLaren team.

"Both sessions today were quite positive," he claimed, "Our car's feeling reasonably good around here, and it's a fun circuit to drive, so I think we can make further progress. Hopefully we can qualify a little nearer to the front, too.

"[While] that will be made more difficult due to my penalty, in terms of race-pace, I think we're looking reasonably good - we just need to extract the maximum qualifying performance from the car. It's a pity that I'll be starting three places further back - I haven't made it easy for myself in the past few races - but I'll be giving it everything I've got [in qualifying] tomorrow."

While Button's problems were self-made, soon-to-depart team-mate Sergio Perez had issues with his MP4-28 that added to the limit on his day's running. The Mexican, who cites Austin as his 'home' race given its proximity to the border, was told of his impending release from Woking in the build-up to the event, and was glad to be able to put an uncertain future out of his mind for a couple of hours.

"After the past few days, it was really nice to be able to get out on track and do the work that I really love," he confirmed, despite having finished a disappointed 13th on the timesheets.

"We had a mechanical issue today that affected our running - the balance of the car wasn't great, and I didn't feel comfortable. It also cost me quite a bit of time this afternoon and meant we didn't do too many miles on high fuel. Of course, that makes things a little tougher, but with the changes we're set to make overnight, I'm sure we'll improve tomorrow."

Perez also commented on the 'green' nature of the Circuit of the Americas, which he still found slippery where many of his rivals remarked on the improved level of grip of 2012.

"This circuit is quite dirty, so it's difficult to warm up the tyres," Perez explained, "The track surface also changed quite a lot between FP1 and FP2, so I think it'll be very interesting to see if it changes further tomorrow, particularly as more changeable weather is expected."

"Neither Jenson nor Checo enjoyed a smooth day's running today," team principal Martin Whitmarsh confirmed, "Despite these issues, both drivers reported that the MP4-28 performed well around this fantastic Austin circuit. This is a great racer's track, and I'm sure that Jenson and Checo will be pushing hard to achieve optimal qualifying positions tomorrow afternoon.

"Checo's running this afternoon was hampered by a mechanical issue that affected the balance of his car, and also meant that his on-track running was curtailed while we attempted to rectify it. Jenson's was an unfortunate incident, but his race pace looks encouraging, and, racer that he is, he'll not let this setback affect his preparations for Sunday."