The 25-year-old will start the race at the Circuit of the Americas in pole position, while his Spanish rival will be in eighth place.
"We know we are fighting for the championship," Vettel told reporters. "We know the situation well, people like you are so kind and remind us all the time.
"It doesn't really matter where he is going to be in the race; we have to focus on ourselves and get the best possible result.
"If you go around thinking about where the other car is you don't do your optimum and we want to be the optimum because that enlarges your chances of doing well tomorrow and winning the championship this year."
Vettel leads Alonso by 10 points in the world championship title race.