Max Verstappen dominated practice at the Mexico Grand Prix on Friday, ending the session over a half a second ahead of world champion and title rival Lewis Hamilton.
The Dutch Red Bull driver, who has a 12-point lead over Hamilton in the championship with five races left, clocked a blistering 1min 17.301sec.
That was 0.424sec ahead of Valtteri Bottas and 0.509sec faster than Hamilton in the second Mercedes.
Red Bull's Sergio Perez, racing in front of his home fans at the spectacular Autodromo Hermanos Rodriguez, was fourth at 0.570sec behind his teammate.
Ferrari's Carlos Sainz, 1.017sec back from two-time Mexico GP winner Verstappen, filled out the top five.
"It was a solid session for us," Red Bull boss Christian Horner told Sky Sports.
"Both drivers are starting to find a setup that they're liking, the short runs and long runs look reasonable.
"I think Mercedes have still got a bit in the pocket so I don't think we've seen their full potential, but focusing on ourselves it was a reasonable day."
Bottas had edged out Hamilton in the morning session in a best time of 1min 18.341sec, mastering the tricky, dusty conditions.
Verstappen and Perez had been third and fourth fastest respectively at 0.123sec and 0.269sec.
"We're giving it absolutely everything we've got, they're just quicker than us at the moment," said Hamilton at the end of a frustrating day.
Hamilton and Kimi Raikkonen in an Alfa Romeo, meanwhile, had been put under investigation for not having followed the instructions of the race director to rejoin the track after coming off at the first turn in the opening session.
Both men escaped with a reprimand.
Lance Stroll of Aston Martin and Japanese driver Yuki Tsunoda of AlphaTauri will start from the back of the grid in Sunday's race for taking too many engine parts after both also changed engines.
2nd session times:
Max Verstappen (NED/Red Bull-Honda) 1:17.301 (28 laps), Valtteri Bottas (FIN/Mercedes) 1:17.725 (31), Lewis Hamilton (GBR/Mercedes) 1:17.810 (26), Sergio Perez (MEX/Red Bull-Honda) 1:17.871 (26), Carlos Sainz (ESP/Ferrari) 1:18.318 (29), Pierre Gasly (FRA/AlphaTauri-Honda) 1:18.429 (29), Charles Leclerc (MON/Ferrari) 1:18.605 (28), Yuki Tsunoda (JPN/AlphaTauri-Honda) 1:18.644 (31), Sebastian Vettel (GER/Aston Martin-Mercedes) 1:18.681 (32), Fernando Alonso (ESP/Alpine-Renault) 1:18.732 (27), Kimi Raikkonen (FIN/Alfa Romeo Racing-Ferrari) 1:18.841 (25), Lando Norris (GBR/McLaren-Mercedes) 1:18.979 (27), Antonio Giovinazzi (ITA/Alfa Romeo Racing-Ferrari) 1:19.227 (31), Esteban Ocon (FRA/Alpine-Renault) 1:19.431 (37), Daniel Ricciardo (AUS/McLaren-Mercedes) 1:19.521 (7), Mick Schumacher (GER/Haas-Ferrari) 1:19.620 (30), Lance Stroll (CAN/Aston Martin-Mercedes) 1:19.730 (36), Nicholas Latifi (CAN/Williams-Mercedes) 1:20.820 (17), Nikita Mazepin (RUS/Haas-Ferrari) 1:21.581 (28), George Russell (GBR/Williams-Mercedes) 0.000 (2)