Kimi Raikkonen says he is determined to fight to keep third place in the Formula 1 world championship after what he labelled as an "OK day" at Austin.
The Lotus driver looked in contention for a podium finish early in the race after starting from fourth, but as the track got cooler he struggled for pace and eventually dropped to sixth position.
The Finn is now 16 points ahead of race winner Lewis Hamilton with just the Brazilian Grand Prix to go.
Raikkonen, who had won the previous race in Abu Dhabi, admitted it had not been an easy day for him.
"It was an OK day, but not a very easy one for us," he said. "I got a bad start and then I touched with a Force India at the second corner so I lost a few more places. After that the car was OK and I could get past some of the others.
"Unfortunately, when it got cloudy it got too cold so the tyres stopped working and that's where we saw Jenson [Button] get past. Basically, it was a race where we were just depending on the tyres to be in their window.
"I'm still third in the championship and we'll do everything we can to maintain this position until the end."
Team-mate Romain Grosjean also looked strong during parts of the race, but wound up seventh after spinning out while fighting for position with Force India's Nico Hulkenberg.
"Not a bad race but the spin on lap seven was frustrating," he said. "The start was good, the first lap was good and the pace was definitely there.
"I recovered pretty well from where I was to finish P7 and was fighting Kimi at the end which is a positive sign.
"I pushed as hard as I could, so I was happy to bring home some more points for the team."