File photo Ferrari's Sebastian Vettel. Photograph:( Reuters )
Hamilton has won five of the six races held at the Circuit of the Americas, with Vettel the only other driver to triumph there.
Sebastian Vettel recognised on Thursday that he and Ferrari had made mistakes this season but refused to single out the moment where his hopes of winning a fifth Formula One title ended.
The German is 67 points behind Mercedes rival Lewis Hamilton, who can instead become a five-time champion in Texas on Sunday.
The Briton has won six of the last seven races, and is chasing a fifth in a row.
Asked at the US Grand Prix whether he accepted Mercedes had done a better job than Ferrari, Vettel was clear: "So far, yes. It's pretty obvious. You just have to look at the points.
"I should have done better. If you want to name one (race), then Hockenheim," he added.
"Maybe we should have done better, but overall we just didn't have enough races where we had the speed to dominate the weekend and put the car on pole and finish first."
Vettel, winner of five races so far this year, led at his home German Grand Prix at Hockenheim before skidding off a wet track and into the barriers. Hamilton went on to win.
The German's first retirement of the year cost him the championship lead at a crucial point but he questioned the significance of it.
"I am not a believer in this has been the turning point or the stars have been wrongly aligned and all this. I don't believe it," he said.
Hamilton will be champion if he scores eight points more than Vettel, something he has done for the past four races with Mercedes now chasing a hat-trick of one-two finishes.
"I don't think it's much point now to start thinking too much about what happened," said Vettel on the situation.
"I think it's still something that we have in our hands to change and that's what we look for."
Asked what his approach would be to the weekend, which promises to be wet and cold, Vettel said it was simple.
"We are quite some points behind, we focus on winning and then we see what the others are doing, so it's quite straightforward to be honest," he said.
"Generally I always try to win so I think you have to be aggressive to win. And of course you need to find the right balance so obviously you never try to do something silly or not to finish because that way you can't win," he said.
"I know what it takes, I know what to do...but for sure we know we need to take probably here or there a bit more risk because we are not in the position to manage the gap in the championship, because we don't have a gap."
Vettel said the previous race in Japan had helped Ferrari understand more about their car and hoped Austin could see a return to form.
Hamilton has won five of the six races held at the Circuit of the Americas, with Vettel the only other driver to triumph there -- with Red Bull in 2013.