Ahead of today's opening session the air temperature is 23 degrees C, while the track temperature is 47 degrees.

Now we are unsure just how much importance the teams place on this particular event, but in case you haven't been reading the previews, there are no less than 9 reserve drivers on duty in this session. That's right, nine!!!

Pato O'Ward replaces Norris at McLaren, Antonio Fuoco is in for Hamilton at Ferrari, Fred Vesti for Russell at Mercedes, Arvid Lindblad for Verstappen at Red Bull, Jak Crawford for Stroll at Aston Martin, Paul Aron for Gasly at Alpine, Ryo Hirakawa for Bearman at Haas, Luke Browning for Sainz at Williams and finally Ayumu Iwasa for Liam Lawson at RB.

In terms of updates, Ferrari has new Cooling Louvres and a new Rear Corner. Both are specific to the requirements of the circuit, with the new bodywork exit louvres extending the top end of the engine cooling capacity, at the expense of car efficiency. As for the engine cooling options, this update targets an increased cooling capacity for the rear brakes to cope with the requirements of the track.

In its quest to help Max Verstappen win the title, Red Bull has brought a new Front Corner, Engine Cover, Floor Body and Edge Wing. Given the rigours of brake cooling in the reduced atmospheric pressure of Mexico City, larger inlet and exit caps have been prepared for this race to simply recover air mass flow. As for the engine cover, in work carried out for the previous cooling revision, more benefit was found from redistributing the exit air and given scope to introduce via an update to existing tooling, this can be deployed in Mexico. In addition, a wider louvre exit panel is available to recover mass flow in the ambient conditions encountered. As a make from the previous specification of floor, a new upper surface rearwards of the outer floor fence plus sidepod split line are offered, the latter to accommodate the sidepod revision. These offer the cooling benefit noted above a small increase in load. Finally, to draw benefit from the lowered upper floor surface and made from the previous edge wing specification, a revised leading edge region extracts a little more load whilst maintaining flow stability.

Alpine has a new Coke/Engine Cover. As a consequence of the high cooling demand of the track, the bodywork exit has been updated to increase the air flow through the coolers.

Racing Bulls have a new Coke/Engine Cover and Cooling Louvres. The main cooling exit at the rear of the bodywork has been enlarged, to increase the available engine cooling, while the louvre panels used at circuits with high engine cooling requirements have been made larger to increase engine cooling.

Williams also has new Cooling Louvres. The increased number/size of the louvres increases the flow of air through the cooling system, which helps compensate for the relatively low air density in Mexico City. The higher cooling panels have a negative effect on downforce and drag and therefore will only be used if necessary to cool the PU in the ambient conditions of this weekend.

New Cooling Louvres for Sauber also due to the increased mass flow rate required for the particular ambient conditions here. This update provides a higher maximum cooling level.

The lights go green and Vesti leads the way, followed by Fuoco, Antonelli, Hadjar and Colapinto.

As more drivers emerge most are on hards, though Hadjar, Ocon and Hulkenberg have opted for mediums.

Of the first wave, Hadjar goes top (22.001), ahead of Tsunoda, Piastri, O'Ward and Colapinto.

Ocon goes top with a 21.884 as Leclerc goes second and Albon third.

A 21.570 puts Piastri (hard) at the top of the leaderboard. However, Hadjar (medium) responds with a 21.091.

Lindblad goes fifth with a 21.911, to go quickest of the 'rookies'. However, Vesti responds with a 21.670 to go fourth.

Quickest in the final two sectors, Ocon crosses the line at 20.934 on the mediums.

Hulkenberg goes top with a 20.128 on the mediums, ahead of Ocon and Tsunoda, however Hadjar demotes them all with a 20.128. Ass one would expect medium runners fill the first three positions.

That said Tsunoda goes second with a 20.495 on the hards.

Antonelli goes third as Fuoco remains rooted to the bottom of the leaderboard.

Antonelli goes top with a 20.035, ahead of Hadjar, Ocon and Tsunoda. Browning, tenth, is currently the leading 'rookie'.

With 35 minutes remaining, Piastri, currently sixth, 0.699s off the pace, is the first to switch to the red-banded rubber. He subsequently posts a 19.035, an improvement of 1.7s on his best time which was set on the hards.

Antonelli switches to the softs, as do Hulkenberg, Leclerc, Vesti and Hirakawa.

Albon (mediums) goes second with a 19.384.

Antonelli goes top with an 18.487, just moments after Piastri had improved to 18.784.

Leclerc (softs) goes third but is demoted when Hulkenberg goes second with an 18.760.

Alonso improves to seventh on the softs, the Spaniard clearly struggling with his car.

An 18.380 sees Leclerc go top, 0.107s up on Antonelli.

Fuoco, who is among the busiest of drivers, remains twentieth, 3.6s off the pace.

Hadjar has to perform a three-point turn after going off at Turn 12 after locking-up.

Having slipped to fourth, Piastri switches back to hards - having avoided mediums - to begin his race sim.

In twelfth, Vesti is currently the fastest 'rookie', ahead of O'Ward and Aron.

Leclerc follows Piastri's example and switches back to hards.

Lindblad goes sixth with an 18.997, ahead of Tsunoda (8th) and Hadjar (11th).

Piastri has a big moment on the dusty track but keeps it all together. Sems he was on an out lap on softs again.

Understandably, the 'rookies' are not taking any risks, though they are effectively in the shop window none of them wants to mess things up for the drivers they are replacing, particularly so in the cases of Lindblad and O'Ward.

The session ends. Leclerc is quickest, ahead of Antonelli, Hulkenberg, Piastri, Bortoleto, Lindblad, Ocon, Tsunoda, Colapinto and Albon.

Hadjar is eleventh, ahead of Alonso, O'Ward, Vesti, Aron, Hirakawa, Iwasa, Browning, Crawford and Fuoco.

Check out our Friday gallery from Mexico City here.