Russell tops crash-hit first practice at Mexico Grand Prix
The session was stopped twice by red flags, once for debris that had fallen onto the main straight and once for a crash involving Williams' Alex Albon and Ferrari's Oliver Bearman, a reserve standing in for Charles Leclerc for the session.
Both drivers were unhurt.
Yuki Tsunoda was third for RB ahead of defending three-time world champion and series leader Max Verstappen of Red Bull, Nico Hulkenberg of Haas and McLaren's Oscar Piastri.
Esteban Ocon was seventh for Alpine ahead of Sauber's Valtteri Bottas, RB's Liam Lawson and local hero Sergio Perez who was 10th in the second Red Bull.
After a busy morning, during which McLaren submitted a request for right of review of the penalty given to Lando Norris in Austin last Sunday, the opening session began in bright sunshine with an air temperature of 23 degrees Celsius.
Five rookies were involved including Pato O'Ward at McLaren, in Norris's car, Kimi Antonelli in Lewis Hamilton's Mercedes, Felile Drugovich in Fernando Alonso's Aston Martin, Bearman in Leclerc's Ferrari and Robert Shwartzman in Zhou Guanyu’s Sauber.
A roar greeted Perez, who had admitted he was enduring a "terrible season" on Thursday, for his opening lap and almost immediately the session was red-flagged after debris was left across the main straight.
Antonelli ran over it and Verstappen reported also hitting debris.
It was unclear where the debris came from as a marshal suggested it may have fallen from an overhead bridge, but this was unconfirmed.
After a 10-minute delay, the action resumed with Russell going top before a big crash involving Albon and Bearman at Turn 10. Albon lost his car on a kerb at Turn Nine and slid into Bearman before hitting the barriers.
After a further 10-minute break, the action resumed with Sainz setting the pace ahead of Russell, who returned to the top in 1:17.998 with 20 minutes remaining in an almost breathless session at the high-altitude circuit.
Russell's lap time was almost six-tenths clear of Sainz and eight-tenths better than Verstappen.
The Dutchman goes into the weekend with a 57-point lead over Norris in the championship race after extending his advantage in Texas last weekend.
The McLaren driver was penalised and lost third place to his title rival for running off the track as he overtook Verstappen.
