Lewis Hamilton's quest to secure a sixth Formula One world championship in Mexico received a controversial boost after Max Verstappen was stripped of pole position.
Verstappen was dealt a three-place grid penalty for failing to slow under yellow flags following Valtteri Bottas's last-corner crash. The Dutchman's punishment moved Hamilton up to third on the grid.
Hamilton must finish at least on the podium on Sunday to stand any chance of taking the title. Charles Leclerc assumes pole with Sebastian Vettel forming an all-Ferrari front-row.
Hamilton will win the championship at the Autodromo Hermanos Rodriguez if he outscores Mercedes teammate Bottas by 14 points.
Bottas is expected to start from sixth despite sustaining extensive damage to his car.
The stewards initially chose not to investigate Verstappen, but launched a probe following comments made by the Dutchman in the post-qualifying news conference.
Asked if he had slowed down to acknowledge the yellow flags deployed after Bottas's accident, he replied: "Didn't really look like it, did it? No."
Verstappen was then called before the stewards – and more than three hours after securing only the second pole of his career, he was pushed back to fourth. Verstappen was also hit with two penalty points on his licence.
A statement from the FIA read: "The stewards heard from Verstappen and the team representative and have reviewed video, audio and telemetry evidences which clearly showed that the driver attempted to set a meaningful lap time and failed to reduce his speed.
"Verstappen admitted that he was aware that Bottas crashed and did see the car on the left-hand side of the track, but was not aware of the waved yellow flag. He also admitted not reducing his speed.
"The stewards noted from the on-board images that the waved yellow flag was clearly visible and was shown with enough notice. The previous driver (Vettel) reduced the speed significantly as per the regulations."
The stewards' verdict will come as a boost to Hamilton, who had earlier called on Formula One's governing body to punish Verstappen.
"It is really important that the FIA are very strict on yellow flags," he said. "There could have been marshals on the track.
"These volunteers put their lives on the line to make sure we are safe on the road and you have got people who are being careless and not abiding by the rules. Max didn't need to stay flat-out, he had already got pole.
"A double yellow flag means slow down; there could be a massive incident ahead. The fact that he ignored it is not great. Hopefully the right calls are put in place so the drivers know to respect these things."
Bottas, Hamilton's sole challenger for the championship, hit the wall before slamming into the advertising hoardings in the closing moments.
The Finn took a number of deep breaths on the radio and remained in his car for some moments, but eventually walked away from the accident. He was taken to the medical centre before he was given the all-clear.
"It was quite nasty actually in the end," said Bottas. "I hit my knees together. For the first five minutes after the accident I couldn't feel my right knee but there is no pain now."
Mercedes boss Toto Wolff added: "Valtteri's car is pretty damaged but we are 90 per cent confident we can fix it without any penalties. We got away with it."
