Michael Schumacher billed qualifying as "better than expected" but it was all-change on Sunday as he admitted his US GP was "worse" than expected.
The seven-time World Champion started the Austin race from fifth on the grid but lap after lap was overtaken by faster drivers as his W03 ate through his tyres.
As a result Schumacher was one of just two drivers who came in for two pits stops, dropping well down the order.
After 56 laps the German had plummeted from fifth to 16th.
"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," he said.
"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."