Max Verstappen was defeated by his rivals during FP1 in Mexico as two F1 stars clashed.
The Red Bull star finished P4 in the session, but it was issues with his power unit that would have worried Verstappen as he was forced to retire towards the end of FP1.
"There’s something wrong with the engine mate. I don’t know… it’s not behaving nice!” Verstappen reported to his team.
If Red Bull's engine problems persist, it could provide a further issue to Verstappen's Mexican GP weekend, particularly if McLaren can capitalise on their struggles.
However, it was George Russell and Carlos Sainz who set the top two times in FP1 as they look to have an early advantage.
VCARB star Yuki Tsunoda completed the top three, setting a time half a second quicker than Sergio Perez in the Red Bull.
The session had barely begun before a red flag was waved due to a piece of debris left on the track, with Kimi Antonelli running over it in Lewis Hamilton's Mercedes.
A second red flag was brought out halfway through the session when Alex Albon and Ollie Bearman, competing for Ferrari in place of Charles Leclerc, collided.
The Williams crashed out at Turn 10 with the Ferrari parked further down the road with suspension damage, after Albon approached the slowed down Ferrari at high speed and lost his car.
Albon swiped Bearman's car as he lost control which forced both drivers out of the session, returning to the garage.
Ferrari now sit just eight points behind Red Bull in the constructors' standings, so the performance of both teams in Mexico is vital to the 2024 championship.
FP1 in Mexico also featured five rookies with Antonelli replacing Hamilton, Bearman standing in for Leclerc, Pato O'Ward driving instead Lando Norris, Felipe Drugovich for Fernando Alonso and Robert Shwartzman replacing Zhou Guanyu at Sauber.