The Mercedes driver started the Austin race from fifth position but quickly dropped down the order as he struggled with a lack of grip.
Eventually the German finished in 16th place as Mercedes continued with its pointless streak, now going for five consecutive races.
"I can't find any words other than ironic ones for the race today - there was a lot of action around me but unfortunately in the wrong direction," said Schumacher.
"To say that the race was a real struggle would be an understatement. I couldn't get any grip from my first set of tyres, and there must have been some kind of damage for them to perform so badly.
"We had to change our strategy to two stops which then compromised our race even further. All in all, it was much worse than expected today, especially considering that things did not look that bad yesterday and Friday."
Team-mate Nico Rosberg also had a tough day from 17th on the grid, the German at least finding some consolation in the fact the team learned lessons for its 2013 car.
Rosberg used an older spec car for qualifying and the race and he finished in 13th position.
"It was a difficult weekend for us and unfortunately we weren't able to score any points today. However we have learned some important lessons for next year and that's what counts at the moment.
"I hope we can be more successful next year here in Austin as I have enjoyed our visit. The track, the people and the city are absolutely fantastic. So I look forward to coming back here in 2013 and we will work hard next weekend to finish the season on a positive note."