Lando Norris led the way in Las Vegas in a second practice session suspended for 19 minutes due to a loose drain cover.
Norris, who holds a 24-point championship lead heading into the concluding three rounds of the season, saw off Mercedes’ Kimi Antonelli by 0.029 seconds on the Strip.
Max Verstappen, 49 points back in the title race, finished ninth with Norris’ McLaren team-mate Oscar Piastri only 14th.
However, the second running of the night was red-flagged twice amid reports of a dislodged drain cover at the 17th and final corner.
The stoppages drew flashbacks to the first event staged here two years ago when a drain cover broke free and tore into Carlos Sainz’s Ferrari at 200mph.
The one-hour session here on Thursday was initially stopped at 8.38pm local time.
A statement from F1’s governing body, the FIA, read: “Following a marshal report of a possible loose manhole cover before Turn 17, race control were unable to confirm this information from the CCTV available.
“The session has been red flagged as a precautionary measure and race control personnel are currently on site assessing the situation.”
A 16-minute delay followed before the pit-lane re-opened for the concluding six minutes with the FIA saying they were “confident” all was in order.
But the cars were back on the street circuit for just three minutes when another red flag was deployed.
A second FIA statement read: “Some race control personnel remained on-site when the session was restarted.
“They reported that the manhole cover was moving as cars passed over it, which led to the session being ended under red-flag conditions. Further inspections are underway.”
The race in Las Vegas is the only one on the calendar which is promoted by F1’s American owners Liberty Media. The international television feed – controlled by F1 – did not show the affected part of the track during either delay.
The interruptions contributed to a distorted timesheet with a number of top drivers failing to post a representative lap on the quickest soft tyre compound.
The season is reaching its climax in Las Vegas with only rounds to follow in Qatar and Abu Dhabi.
McLaren have largely been the class of the field this year but the street circuit on the Strip has not been a venue which has suited their machinery in the previous two races staged in Nevada.
In the opening running of the weekend, Norris ran wide twice at Turn 12 on two quick laps, and finished only sixth. But the Englishman, bidding to win his first world championship, will be encouraged by his speed in the day’s interrupted concluding session.
