Haas could have had a shock podium finish in the Brazilian Grand Prix but for a baffling MGU-K glitch, reckons team principal Gunther Steiner.
Grosjean was running seventh under the penultimate safety car but was pushed wide by Carlos Sainz Jr - who went on to finish third - at the restart and tumbled down the order to finish 13th.
Steiner revealed that Grosjean's fate was sealed because his MGU-K failed to work at the exact moment it was needed for the battle with Sainz.
"He couldn't get going," he said. "And then Sainz pushed him off as well. Then you just go back into the mix again. Our car in the traffic isn't good so we just lost all these positions, and then it was like square one.
"It was only on that restart that there an MGU-K failure.
"It's unbelievable to me."
Rather than the MGU-K problem being an out-and-out failure, Steiner said the glitch was only temporary - which made the situation even more baffling.
"It was kicking out," added Steiner. "He had no power from the MGU-K, and then the next acceleration was cutting out and then it was good again.
"Nobody knows what it is. We still don't know because afterwards it worked again."
Grosjean admitted that it was typical of Haas to have suffered such misfortune at the very moment it could have produced something special.
"It was honestly one of my best races," he said. "I really drove it like flat out every single lap to the limit.
"But when the safety car came I knew we were dead. The tyre temps just dropped, I lost 40 degrees on the front-right tyre and I knew the restart was going to be tough.
"I was not very happy with Sainz, pushing me very wide in Turn 2, but even so then people on soft tyres behind me just passed me all the time.
"So one more time it's our luck, when we can go for points, when we look good for points, we just get bad luck.
"I'm happy for Pierre [Gasly, who finished second]. That's the positive of the afternoon.
"He deserved that podium, I was the last Frenchman to stand on the podium. So good for him."