The sudden downpour of rain that hit the race on the 30th lap at the Brooklyn Street Circuit precipitated leader Nick Cassidy aquaplaning into the wall at Turn 6, into which di Grassi followed him.
Stoffel Vandoorne then also crashed into the stricken pair of cars, which ultimately caused the red flag that put the race on ice - before the decision was made not to restart.
Di Grassi said that prior to the incident, he had been on the radio complaining that conditions were "undriveable" before the crash unfolded between the trio.
He reckoned that he'd collided into Cassidy's car at around 100kph, and praised the safety structures onboard the Gen2 Formula E cars that meant all three drivers walked away unharmed despite significant damage.
"The cars were aquaplaning too much, even on the straights we had aquaplaning. And I went to the radio and said that it's undriveable, it's not safe to drive," di Grassi recalled.
"And the call from the FIA came a bit late, which caused the big crash at corner six.
"Thankfully these cars are extremely safe because this was the probably the biggest crash of my Formula E career. Not probably, it was the biggest crash of my Formula E career today.
"And I'm without any problems; the car is pretty much destroyed, but that shows how safe these cars are.
"I crashed into Nick at least at 100kph, and then Stoffel crashed into me at a similar speed. So I'm very happy with the safety of the car and zero bruises and happy that all the other drivers also are 100%."
Di Grassi reckoned that before the rain, the race had been "non-eventful" from a Formula E standpoint and that the cars around him were all on a similar energy level.
He explained that he would have been interested to see how all of the leading cars would manage the final part of the race with regards to energy management.
"I was chasing Nick for a great part of the race, and was also fighting a really long fight with Stoffel. I lost one position to him but gained it back.
"But it was non-eventful race to Formula E standards. And everybody had a very similar pace, very similar energy around myself.
"I think by the last laps it would be very interesting to see who had the best temperature management and start to show the energy and the car balance.
"Then the rain came and then we could see every lap the cars were sliding more and more."
