Stroll and Alonso were involved in a huge crash on the back straight on lap 22 of the race that briefly sent Alonso’s Alpine car airborne.
As Alonso moved to the left to pass Stroll, the Aston Martin driver shifted across to defend, only for their wheels to make contact.
It sent Stroll spinning into the wall and out of the race, while Alonso suffered a big impact when his car hit the ground again.
He managed to drive slowly back to the pits and then continued after receiving a new nose and a fresh set of tyres.
Stroll and Alonso met with the FIA stewards after the race at the Circuit of The Americas, where it was decided that Stroll was predominantly to blame for the crash, resulting in a three-place grid penalty for Mexico.
“It was clear to us that the driver of Car 18 made a late move in reacting to the overtaking attempt by the driver of Car 14 by moving to the left,” the stewards said.
“The stewards determine that the driver of Car 18 was predominantly to blame.”
As well as the three-place grid penalty, Stroll also picked up two penalty points on his FIA superlicence, taking him up to five for the 12-month period.
