San Francisco Frontiers - Norris on top in sizzling Austin GP practice

The 25-year-old Briton, bristling after being disciplined internally by McLaren, clocked a best lap in one minute and 33.294 seconds to outpace Hulkenberg by 0.255sec and Piastri by 0.279sec as he bids to close a 22-point gap in the drivers' title race with six events remaining.

Two-time champion Fernando Alonso was fourth for Aston Martin ahead of four-time champion Max Verstappen of Red Bull, Alex Albon of Williams and Mercedes' George Russell.

Seven-time champion Lewis Hamilton was eighth for Ferrari.

All of the leading drivers clocked their best laps on soft slick tyres in the closing minutes except for Alonso, on hards, and Russell, Hamilton and rookie Isack Hadjar, who all used mediums.

The action began with Verstappen leading the way on a hot and sunny day at the sweeping Circuit of the Americas with an air temperature of 33C, enough for the 'heat hazard' rule to be executed, enabling drivers to wear cooling vests in their cars.

Not everyone chose to take a vest, the Dutchman going without because he found it to be uncomfortable and flawed.

As a result, his Red Bull car carried 500 grammes of ballast to ensure he had no competitive weight advantage.

Verstappen was quick to clock an early lap in 1:38.797, which he soon trimmed down to 1:35.426 after Carlos Sainz, Hamilton and Norris had taken the initiative.

Much of the early interest was focussed on the revised special liveries being run by six teams amid fevered reaction to Apple TV's successful bid, of a reported $750 million, to broadcast F1 exclusively in the United States for five years from 2026.

- Revitalised Hamilton -

All of the teams were running on hard tyres -– leaving their softs in preparation for sprint qualifying later on Friday –- with Hamilton, in particular, enjoying himself in what seemed to be a revitalised Ferrari.

The Briton went top again after 20 minutes in 1:34.857, half a second clear of Verstappen with Russell third.

For Norris, this was an important session at a critical weekend as he sought to keep his title challenge on track following internal talks at McLaren over his collision with Piastri on the opening lap in Singapore.

"The team held me accountable for what happened, which I think is fair," Norris said.

"It has been dealt with," said Piastri, without adding details on the latest 'papaya rules' (do what is best for the team) incident.

A mid-session red flag paused the action for five minutes after debris from Lance Stroll's Aston Martin landed on track at the final corner.

On resumption, Sainz was held back for gearbox repairs while Norris improved to take second behind Hamilton, half a second adrift.

With 15 minutes remaining, most drivers pitted for soft or medium tyres.

Verstappen, on softs, clocked 1:33.648 to go top before being beaten by Alonso in 1:33.639, an advantage of 0.009.

Hamilton, on mediums, went fourth in a flurry of late activity that saw Norris romp to top spot in 1:33.294 on softs.

Q.Nelson--SFF