Ahead of today's qualifying session the air temperature is 21.2 degrees C, while the track temperature is 45.8 degrees.
Mercedes worst fears were realised earlier when Sergio Perez and Max Verstappen were almost half a second quicker, leaving Lewis Hamilton clearly incredulous.
While Christian Horner suggested that the German team might have turned its engines down in practice, the world champion's reaction earlier said it all.
Then again, stranger things have happened, and though Red Bull clearly has the pace will it make best use of it today and again tomorrow, and let's not forget things like mistakes, traffic and poor strategy.
Norris, Stroll, Ocon and Tsunoda all head to the back of the grid as a result of engine penalties, however, with the possibility of starting 17th on offer there is still much to play for.
Sainz has looked consistently good thus far this weekend, as Ferrari seeks to claim best of the rest from McLaren.
Of course those penalties offer hope to those driver who usually miss out, and while we don't expect to see a Haas in Q3 we could be in for a few surprises.
For the most part however, the next hour is going to be about Red Bull and Mercedes, and while there is every likelihood of team orders tomorrow there is nothing to prevent Perez claiming a historic pole today.
Given the pace of the Bulls, Hamilton's best hope might be a tow from his teammate, but other than whether Bottas will want to play wingman yet again there is the little matter of traffic.
Indeed, those drivers with penalties could all be called on to assist their respective teammates, though Norris was in no mood to play ball yesterday.
As for tyres, with that advantage, will Red Bull try to make it into Q3 on the mediums... indeed, will Mercedes?
What was interesting earlier was that the softs appeared to be better on the second flying lap.
In the moments before Q1 we have a Mexican Wave around the stadium... well, it is Mexico.
The lights go green and Latifi (mediums) heads out, the Canadian subsequently joined by Schumacher and Mazepin, who are both on softs.
In the Red Bull and Mercedes garages works continues on the cars of Verstappen and Hamilton.
Raikkonen, who has been looking good this weekend, appears to have a lot of support here.
Schumacher gets things going with a 21.524 while Mazepin can only manage 22.270.
Raikkonen stops the clock at 19.108 as Leclerc warns that his power unit "doesn't sound good".
As expected, as drivers attempt to give their teammates a helping tow, traffic builds up accordingly.
Schumacher has his previous time deleted for track limits at Turn 12.
The crowd rises to greet Perez, as Giovinazzi posts an 18.820.
Leclerc goes top with a 17.991 but Norris is on a hot lap.
However, the session is red-flagged after Stroll goes off in the final corner and hits the barriers. Asked if he is okay, the Canadian wearily relies that he is.
Relay shows him fighting to control the car in that fast final corner and spinning around to his the barriers with the front of the Aston Martin.
"Is he okay?" asks Hamilton, who is assured that he is.
This is bad news for the Red Bull pair who have used one set of softs. Indeed, back in the garage there is much work going on on Perez' car which is missing its rear wings, as was the case during FP2 with the other RB16.
Such was the damage to the Tecpro it is a fairly considerable stoppage.
At the time of the crash, Leclerc was quickest, ahead of Vettel, Sainz, Giovinazzi, Raikkonen, Stroll and Mazepin.
The session resumes at 14:33 (local time), with 10:58 of Q1 remaining.
Meanwhile, Raikkonen is to be investigated after the session for a "red flag incident". Replay showing the Finn entering the pitlane after seeing the yellow flags and then crossing back on to the track again.
Ahead of the green light, the Alpha Tauri pair are waiting at the end of the pitlane, along with their Haas counterparts.
Meanwhile it is revealed that the flap on Verstappen's rear wing broke earlier, and damaged the DRS mechanism.
On board with Sainz the Spaniard clearly has an issue. "Nothing, nothing, nothing," he reports as the Ferrari crawls along. "No power!"
Given an instruction by his engineer, Sainz gets going again.
All 19 drivers are on track, all sporting softs.
As Hamilton struggles for grip, the AlphaTauri pair are quickest in the middle sector.
Gasly posts 17.746 and Tsunoda 18.237 to sandwich Leclerc.
Hamilton crosses the liner at 17.576 and Bottas 17.516, but Verstappen is on a very quick lap.
Perez posts a 17.451, but even before the crowd can rise to its feet Verstappen responds with a 16.788, a whole 0.663s quicker.
Norris splits the Mercedes pair with a 17.574, as Ricciardo goes seventh (17.719).
While Verstappen pits, the Mercedes continue. Quickest in S1, Bottas improves to second with a 16.959, just 0.171s off the pace. A 17.207 sees Hamilton claim third.
Ocon goes tenth with an 18.126, as Mazepin argues with his engineer. "Are you having a laugh?" asks the Russian when told not to overtake Schumacher. "I'm not having a laugh, Nikita," he is firmly told.
Perez leapfrogs Hamilton with a 17.003, having gone quickest in S2.
With under two minutes remaining, Russell is one of those facing the chop, with Sainz, Vettel, Alonso and Tsunoda hovering.
Sainz goes fifth (17.517) only to be demoted by Tsunoda.
Gasly goes second with a 16.908 but drops to third when Leclerc goes top with a 16.748.
Raikkonen goes eleventh, as Bottas posts a 16.727 to go top.
Quickest, thanks to the evolution of the track in those final moments, is Bottas, ahead of Leclerc, Verstappen, Gasly, Perez, Hamilton, Tsunoda, Vettel, Sainz and Norris.
We lose Alonso, Latifi, Schumacher, Mazepin and Stroll.
Check out our Saturday gallery from Mexico City, here.