Red Bull driver Max Verstappen completed a practice hat-trick for the Mexican Grand Prix after edging out Lewis Hamilton and Sebastian Vettel.
Under overcast skies, and on a drying circuit, Verstappen again held the advantage at the Autodromo Hermanos Rodriguez.
But Verstappen, 21, finished just 0.254 seconds clear of Hamilton, with Mercedes having taken a step forward overnight. Vettel was 0.282 sec off the pace.
Hamilton needs to finish only seventh to be sure of his fifth world championship, while Ferrari’s Vettel must win tomorrow to stand any chance of taking the title fight on to Brazil.
Daniel Ricciardo finished fourth ahead of Kimi Raikkonen, while Charles Leclerc, bound for Ferrari next season, finished an impressive sixth.
Valtteri Bottas stopped on track with a hydraulics problem, and his Mercedes crew now face a race against time to get his car ready for qualifying.
Following a wet start to the session, Hamilton completed just one lap, waving to the crowd, before returning to his garage.
The Briton then took a swipe at the sport’s governing body – and Pirelli for not providing enough tyres for the slippery track.
“I’m sorry to all the fans sitting out there as there’s been no running yet,” he wrote on Instagram.
“The FIA/Pirell won’t give the teams an extra set of tyres to run in these conditions so we are forced to just sit tight and save the tyres we have in case rain comes in qualifying and the race.”
Later, and with the track suitable for dry tyres, Hamilton emerged in the final 10 minutes of the one-hour session to run Verstappen close at the top of the order.
The Red Bull man, however, remains on course to become the sport’s youngest ever pole sitter later on Saturday.
