Hirakawa, 32, replaced Ocon in the first practice session in Mexico and finished 15th before the Frenchman returned for FP2.
Haas announced the drivers' switch three hours before Saturday's third and final practice session around the Autodromo Hermanos Rodriguez, while giving no reason for Ocon's sudden exit and saying that "no further statements will be made at this time."
The veteran driver got into an argument with his race engineer during FP2.
Ocon confirmed after the Azerbaijan Grand Prix in September that he would leave Haas at the end of the 2026 season. He'll be replaced by current Formula 2 leader Rafael Camara.
WEC and Le Mans champion
The Japanese Ryo Hirakawa joined Haas as their reserve driver in 2025 and is a full-time World Endurance Championship driver. The 32-year-old is a two-time world champion in the hypercar class and leads the 2026 championship with 3 wins and 114 points from seven races with his Toyota Racing team, which also includes Mike Conway and former F1 drivers Kamui Kobayashi, Nyck de Vries, Sebastien Buemi, and Brendon Hartley.
He also won the 24 Hours of Le Mans with Toyota in 2022. Hirakawa previously also served as the reserve driver for McLaren and Alpine.
