The 25-year-old Kawasaki rider fell in heavy rains and banged his head against the race course in the opening lap. Handicapped by continuous rain and poor vision, fellow Italian rider Lorenzo Zanetti then struck Antonelli on the ground.
Antonelli subsequently succumbed to the injuries and died at a hospital.
The race was immediately red flagged with the stewards cancelling all the other races for the day.
Mahi Racing Team India rider and defending world champion Kenan Sofuoglu could not believe the news of Antonelli's demise with whom he had breakfast before the race this morning.
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"He was one of the most talented rider amongst the younger lot and very courageous as well," said Sofuoglu, who was looking to register his second consecutive victory in the championship in Moscow after Italy.
Mahi Racing's Chairman Arun Pandey also expressed his condolence to the riders' family.
"It is quite a sad day for the World of motorsports and just shows how much is at stake when the riders get on the track," he said.
"We are only at the half way stage of the competition and I am confident about retaining my title.