Formula One world champions Lewis Hamilton and Kimi Raikkonen collected reprimands on Friday for going off track and then failing to return correctly in first practice for the Mexico City Grand Prix.
Three reprimands in the course of a season trigger a 10-place grid penalty, but Friday's was a first of 2021 for both drivers.
Stewards found Mercedes' Hamilton, the sport's most successful driver of all time, and Alfa Romeo's Raikkonen, who holds the record for race starts, had gone off to the left between turns one and two before rejoining.
They should have rejoined to the left of a bollard at turn three, according to the race director's instruction, but failed to do so.
Seven-time world champion Hamilton is 12 points behind Red Bull's Max Verstappen with five races remaining.