Mercedes was forced to turn down its Formula 1 engine during practice for the Mexican Grand Prix “as a precaution” to combat overheating issues.

Lewis Hamilton and teammate Valtteri Bottas struggled for pace throughout Friday’s running at the Autodromo Hermanos Rodriquez as Red Bull dominated proceedings.

Mercedes ended the day with the seventh and ninth quickest times, having finished well over a second down on Max Verstappen’s session-leading time in FP2.

It has since emerged the reigning world champions faced overheating problems “in a number of areas” of its power unit as a result of the high level of strain placed on engines in Mexico due to running at the high-altitude circuit.

“This is an unusual track, which places unusual demands on the chassis, power unit, cooling systems and tyres,” Mercedes technical director Allison explained.

“From all our running today, we have to conclude that we have not yet found the best way to meet those unusual demands with good performance on both single laps and in the long runs.

“We were overheating the power unit in a number of areas today, and that meant we had to protect against this by turning it down as a precaution.

“With a bit luck, and no little hard work, we can get ourselves into better shape tomorrow and on Sunday, when conditions are also forecast to be cooler.

“We have plenty of work ahead of us overnight and in FP3 tomorrow to put ourselves in a stronger position than we were able to achieve today.”

Bottas admitted the team was left “scratching our heads” after an unusually uncompetitive showing, adding there is no “definitive answer” to Mercedes’ struggles.

"Both of the compounds started to grain quickly and it feels like we're lacking overall grip, so the car is sliding around a lot which is then wearing the tyres,” Bottas said.

“We don't have a definite answer why the pace isn't quite there yet; we're going to have to analyse it and look at it from every angle.

“We have plenty of work to do for tomorrow and, while we are scratching our heads a little at this point, I'm confident that we'll find answers over the course of the evening and come back stronger tomorrow.”