Ferrari's Charles Leclerc led the way in US Grand Prix practice on Friday, with Mercedes' Kimi Antonelli a close second ahead of a race that could make him Formula One's youngest champion.
Leclerc set the pace of one minute 35.291 seconds in a sunny second practice at Austin's Circuit of the Americas after also lapping fastest in the earlier session with a time of 1:36.052 in his upgraded car on a bumpy track.
"It has been a very clean Friday for me, but the others seem to be gaining more than us from Friday to Saturday and seeing the little gap there is, it is not going to be so easy tomorrow," Reuters quoted him as saying.
Antonelli, the 20-year-old who must win on Sunday to have a first chance of taking the title, was fifth in session one when Red Bull's Max Verstappen was closest to 2024 winner Leclerc.
The Italian, who complained about his seat moving, then improved to second place and ended the day 0.042 off the pace.
"We didn't have the best FP1 session, with the car balance not in a great place," said Antonelli, who is 102 points clear of closest rival and teammate George Russell. "We were able to improve that for FP2 though and we took a good step forward."
Verstappen, winner in Austin last year, is chasing his third successive victory after Singapore and Malaysia. He ended second practice as the third fastest and 0.189 off Leclerc with Ferrari's Lewis Hamilton fourth and Russell fifth.
"We tried a different direction with the set-up, but I wasn’t comfortable in the car, especially over the bumps," said Hamilton. "Charles showed there’s pace there, so we need to understand how we can get the car into a better place on my side."
Russell had a black-and-white warning flag for an incident with Leclerc that led to the Monegasque going off track early in the second session, but stewards decided against any further action.
McLaren's reigning champion Lando Norris was third fastest, 0.245 off the pace, in first practice and then seventh later on and behind Racing Bulls' Liam Lawson.
"I think Lando is definitely a lot quicker than his lap time," McLaren boss Zak Brown told Sky Sports television. "He didn't get his third sector in. His first two sectors were very strong.
"So I think we are much quicker than we looked. I think Ferrari's lap time, Mercedes' lap time, there or thereabouts."
Norris sounded less sure: "The pace is not bad. We seem a step away from Red Bull and Ferrari, probably Mercedes as well, but the car is very difficult to drive, too difficult to be consistent and get a nice feeling consistently."
Teammate Oscar Piastri was eighth fastest, with Red Bull's Isack Hadjar ninth and Haas's Oliver Bearman completing the top 10.
Audi's Gabriel Bortoleto, Racing Bulls' Arvid Lindblad and Alpine's Franco Colapinto all collected grid drops for changes to their power units.
Lindblad will drop five places from wherever he qualifies on Saturday, Colapinto 10 places and Bortoleto 20.
Williams looked to be struggling, with Carlos Sainz 20th and Alex Albon 22nd in practice two.
"The car is a mess right now. It's a mess. I have no confidence in the rear," said Sainz over the team radio.
