Interesting picture of the altitude of the Autodromo Hermanos Rodriguez compared to Mount Snowdon, and Ben Nevis, highest mountains in Wales and Scotland.
The altitude of the racetrack means thin air and this has a bad effect on engines, cooling, and most of all, aerodynamics.
Thinner air also means less drag and this may have helped Ferrari in a one-lap qualifying. The aerodynamic set up to take advantage of this can cause greater tyre wear and this may disadvantage Ferrari in the race.
Also, it is a long run down to the first corner, longest in Formula One, so a good start is needed.