Sainz surprised to be on the pace so quickly

Sainz continued to impress on his Renault F1 debut by taking eighth place in FP3 in Austin, a result which would have translated to sixth on the grid as two drivers ahead have penalties.

On Friday, the Spaniard outpaced teammate Nico Hulkenberg in both sessions, earning 10th place in FP1 and 11th in FP2, although the two drivers were running different aero test programmes.

He was beaten by Hulkenberg in the final practice session, but only by 0.042s. The German has the benefit of the latest spec V6, which has improved performance.

"If you would have told me yesterday I have would been on the pace today immediately I would have signed the paper," Sainz said after his first experience of the car on Friday.

"So I have to be happy with that. It was interesting. To have the chance to drive two different cars in one year gives you a lot of information, a lot of things to feel, to test.

"It has been a very interesting day for me, FP1 in particular, feeling the car in wet conditions and onto dry conditions."

Sainz admitted that despite the Renault having the same power unit as the Toro Rosso he had a lot to get used to.

"What you really want to adapt to is the brakes, to the power steering, to the balance of the car, all these kinds of things I've been adapting to little by little through the day.

"I'm still not 100 percent there yet, still need to leave some space in the back of my mind to feel the different stuff going on in the car, but hopefully as I do more laps it will become more natural, more automatic.

"I will need to keep adapting and keep adapting, and I'm sure at the end of the weekend I will still not be 100 percent. So we need to go little by little like we are doing now, covering all the basics, and hopefully we can be nearly there for qualifying, and nearly there for the race."

Sainz preferred to not give too much away about how the Renault compares with the Toro Rosso he drove up until Suzuka.

"It's something that I prefer to keep to myself because it is an advantage, I'm not going to lie, to know two balances, two different philosophies, two different teams, two different cars, and it is an advantage that I honestly prefer to keep to myself, prefer to keep to my team.

"I also think it's not fair to start comparing publicly car behaviours, or anything like that. I'm going to keep that in my pocket and use it for my benefit."