Mexico City: Charles Leclerc topped the times ahead of his Ferrari team-mate Sebastian Vettel to push the title-scrapping Mercedes men down to third and fourth in Saturday's third and final free practice for Sunday's Mexican Grand Prix.
The Monegasque Leclerc clocked a best lap in one minute and 16.145 to outpace the four-time world champion German by two-hundredths of a second ahead of Valterri Bottas and his Mercedes team-mate and champion-elect Lewis Hamilton.
Hamilton is seeking a podium finish at least to help him outscore his only remaining title rival Bottas by 14 points to clinch his sixth championship crown and third in successive years to be completed in Mexico.
In a session reduced effectively to just a 15-minute dash in drying conditions, Carlos Sainz was fifth for McLaren ahead of last year's Mexico winner Max Verstappen of Red Bull and, remarkably after recovering from illness, Pierre Gasly of Toro Rosso.
Red Bull new boy Alex Albon was eighth ahead of Lando Norris of McLaren and local star Sergio Perez of Racing Point.
On a cool and cloudy morning following heavy overnight rain at the Autodromo Hermanos Rodriguez, the circuit remained damp while, in the paddock, an outbreak of stomach illnesses had claimed Gasly, who was initially unfit to drive for Toro Rosso.
The Frenchman was said to be one of dozens of the travelling F1 circus, including team staff and paddock regulars, who were down with the 'bug' -- regarded by many as an occupational hazard in parts of Latin America.
Albon was soon out on track, trying to make up for lost time on Friday when he crashed, and he was soon followed by team-mate Verstappen. Both swapped quick laps to top the times as a dry line began to emerge.
Little of note happened until the closing stages when, with 15 minutes remaining, Kimi Raikkonen was the first driver to switch to slick softs on his Alfa Romeo.
He was immediately fastest until fellow-Finn Bottas, on mediums, outpaced him.
The rest followed in a blur of activity that included Gasly trying a lap to settle his stomach and Albon lapping quickest until Verstappen trimmed his time followed by Sainz and Bottas in the final minutes.