Vettel has failed to finish two of the last three races in Asia, one due to a first lap collision and the other a spark plug problem, and cannot afford any further unreliability on Ferrari's part.
"Normally we're quick, then when we get to race pace we're often behind the Red Bulls and the Ferraris, but today I believe we were equal with the Red Bulls, so that's better than normal".
In the constructors' championship, Ferrari must outscore Mercedes by 17 points if they are to maintain their slim hopes of winning. The race is a 192-mile contest that will run 56 laps around the track. "I honestly couldn't care less if it's here on the last race, as long as it's done".
With 100 points still available it would be a shame to see a champion crowned this weekend, with only three races left after their trip to Texas.
Vettel is unsure what to expect in Texas, but he is upbeat about Ferrari's chances.
Bottas finished 16 in this race last year and retired in 2015.
"I can always be more aggressive but in the past the tyres haven't necessarily taken it and this year it is looking quite good". Traditionally, Ferrari has been stronger on this combination.
Red Bull's Max Verstappen, fresh from signing a new contract through to the end of 2020, was second fastest in 1:35.065 with Vettel third in 1:35.192.
The track itself is a 5.5-kilometre anticlockwise track, which features dramatic elevation changes, blind and off-camber corners and high-speed changes of direction. The first sector is dominated by a fast and flowing Esses section which has characteristics of both Silverstone's iconic Maggots-Becketts complex and the first sector of Japan's Suzuka circuit.
A victory here for Vettel would not only help to shore up what appear to his fading world title chances, but might prove to an increasingly sceptical world that such an uncharitable view of Ferrari is undeserved. It means that Daniil Kvyat returns to the Toro Rosso fold.
Hartley, who will have a 25-place grid penalty for his debut, stepped into a single seater for the first time since 2012 and looked at home straight away with the 14th best time of the morning.
"There has been a lot of mention of it - not of the kneeling - but just of the whole situation", he added.
I think we could see a someone different podium this weekend with movement and deals affecting several teams on the circuit.