Carlos Sainz said it was an MGU-K failure which caused him to retire from the season-opening Australian Grand Prix.
The Spaniard, who scored no points in Australia for the first time in his Formula 1 career, dropped out of the race on lap 11.
Smoke initially began appearing from the Renault-powered McLaren in the final few turns at Albert Park, but as he tried to make it into the pits, the smoke was joined by flames.
Soon after the race, McLaren CEO Zak Brown hinted at the MGU-K being the cause, with Sainz later confirming that theory.
Carlos Sainz's McLaren bursts in to flames 🔥
— Formula 1 (@F1) March 17, 2019
“Yeah, we were starting far back, but we got into contention early on,” Sainz told reporters in Melbourne.
“I overtook four cars at the start and I was already 14th. Everything was going to plan.
“Bad luck, we lost the MGU-K and retired, so hopefully all that bad luck is gone for the start of the season.
“The car felt really good and we could have been in the points.”