Michael Schumacher bemoaned a 16th-place finish at the United States Grand Prix as his penultimate race before retirement ended in disappointment.
The seven-time world champion qualified in fifth but was out-performed by his Mercedes team-mate Nico Rosberg, who started 17th but finished 13th.
"To say that the race was a real struggle would be an understatement," said the 43-year-old German.
"All in all, it was much worse than expected today."
In the third and final campaign of his second spell in Formula 1, Schumacher has finished 12 races and retired from seven.
His best result was third place in Valencia on 24 June and that remains his only podium since returning to the sport in 2010.
Schumacher never looked like adding to his five wins at the United States Grand Prix, which was held in Austin for the first time.
"I can't find any words other than ironic ones for the race - there was a lot of action around me but unfortunately in the wrong direction," he said.
"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."
It was a better day for Kimi Raikkonen as the 2007 world champion continued his impressive first season back in the sport after two years out rallying.
Raikkonen followed up his victory in Abu Dhabi with a sixth-place finish to stay third in the drivers' title standings, although he did start in fourth.
"It was an OK day, but not a very easy one for us," said the Finn. "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.
"I'm still third in the championship and we'll do everything we can to maintain this position until the end."
Williams were able to savour a points finish by both drivers for a second consecutive race and the third time this season.
Both Pastor Maldonado and Bruno Senna ended where they started - in ninth and 10th respectively.
"After today's race I'm happy for the team, for the Venezuelan fans and for myself," said Maldonado. "I hope that this will be one of the best racing venues for Formula 1.
"I am looking forward to the last round in Brazil and we are ready to fight again there."
Senna added: "Overall, it was a pretty difficult race but it was good to end with both cars in the points which is what we are aiming for."
Force India's Nico Hulkenberg crossed the line in eighth to secure points for the 10th time this season.
"It was another tough race but very satisfying to have so many good battles and score another four points," said the German, who sits 12th in the drivers' championship.
"I think we squeezed the maximum from the car and should be pleased with what we achieved."