Ahead of today's second session, the air temperature is 25.7 degrees C, while the track temperature is 41.3 degrees. It is sunny and hot.

As was the case last week, this session is mostly given over to tyre testing, though those drivers who handed their cars over to junior drivers earlier - Magnussen, Ocon, Russell, Albon and Tsunoda - will be allowed to devote some time (45 minutes) to their own programmes.

There were two red flags earlier following stoppages for Fittipaldi and then Lawson in the final moments of the session.

The AlphaTauri encountered a brake issue, which appears to be the team's Achilles Heel at the moment, while Guenther Steiner believes Magnussen will need a new engine.

Indeed, in the moments before the session, it is revealed that the new unit is currently being fitted and the Dane hopes to make it our later in the session.

New engines have also been fitted to Ocon's car and Tsunoda's... so that's three drivers who didn't even participate earlier needing a change of power unit.

The lights go green and Verstappen leads the way, followed by Zhou, Bottas, Russell and Ricciardo.

Those drivers allowed a choice are on mediums, while the rest are on prototypes which this weekend are understood to be at the softest end of the range.

Gasly sets the initial pace, ahead of Verstappen, Perez, Hamilton and Russell, who is the first of the non-prototype runners.

A 21.943 sees Sainz go top, however, on the mediums, Russell responds with a 21.742.

Last week the drivers complained about the initial lack of grip when heading out, this being due to the fact that in preparation for next year Pirelli has reduced the maximum heat of the tyre blankets.

Verstappen takes the top spot as Tsunoda goes third on the mediums.

Switching to the softs Russell goes quickest in all three sectors, stopping the clock at 19.970. Tsunoda, also on the red-banded rubber, subsequently posts a 20.798 to go second.

"Loads of sliding... tyres, we're not in a good place," reports Russell.

As Ocon (softs) goes third (21.177), in the McLaren garage Ricciardo is out of his car and the engine cover has been removed.

With just over an hour (yawn) remaining, Albon finally heads out... on softs. He immediately posts a 22.447 to go 13th.

Shortly after, Magnussen heads out for the first time also.

Oh dear, Leclerc is off and in the barrier at Turn 8 after losing the rear end.

Asked if he is OK, the Monegasque replied: "I am... but not the car."

The session is red-flagged as the Ferrari, which has received significant damage at the rear, is removed and the barrier repaired.

As we reach the half-way point, memories of Ricky Gervais' 2021 Golden Globes monologue comes to mind - the bit where he stares at his watch and sighs.

The session resumes with 38 minutes remaining. Verstappen is first out followed by Magnussen, Gasly, Vettel and Perez as now all drivers are devoted to the tyre test.

"Is there any forecast of rain," asks Latifi," it looks quite ominous." "It won't get to us," he is told. It certainly has clouded over.

Alonso, currently 11th, is really struggling to keep his car on the black stuff.

Asked why the prototypes don't appear to be as quick as the current tyres, Mario Isola explains: "During the test they are not pushing at the limit. These tyres should give them less understeer, it's one of the priorities for next year. We ask them not to change the set up, so we can compare the prototype across different teams.

"They are testing compounds at the C3, C4 level," he adds, "soft compounds, which are good for this track. We want to close the gap between the C1 and the C2. The C3 is closer to the C4, we want a C3 that is closer in the middle. We want the same gap between the levels of compounds."

"We wanted to test in Suzuka, a high energy track that is more representative," he admits. "Here the track evolution is huge, just earlier it was less than expected. In Austin we were happy with the data, this track is different as it is all about traction and braking. It is good to have two tests in two different situations."

With less than two minutes remaining, Zhou stops at Turn 13.

"Hydraulic failure," he reports. "Stop the car," he is told.

The session is red-flagged and will not resume.

Russell is quickest, ahead of Tsunoda, Ocon, Hamilton, Perez, Verstappen, Leclerc, Sainz, Bottas and Gasly.

Alonso is eleventh, ahead of Vettel, Albon, Norris, Ricciardo, Stroll, Schumacher, Magnussen, Latifi and Zhou.

Check out our Friday gallery from Mexico City here.