It was only when the coroner's van arrived and the emergency crews picked him up that they discovered he was warm and had a very weak pulse.
An ambulance returned to the scene, and took the man to hospital.
Ambulance Victoria said it had launched an investigation, but added that both paramedics were very experienced.
One had been doing the job for more than 15 years, and trained other paramedics.
They were said to be devastated about what had happened.
Trevor Oliver, a tow-truck driver who was called to the scene, told Melbourne radio yesterday that he saw movement inside the Porsche before the driver was removed.
Then, after he was laid on the ground with the tarpaulin over him, Oliver said his limbs were twitching.
"I didn't say anything at the time," he said. "I just thought the ambulance had pronounced him dead and that was that, really.
"It was when they went to remove the body into the coroner's van that they noticed that the driver had a very weak pulse."
Simon Thomson, a spokesman for Ambulance Victoria, said it was an "exceptionally rare" case.
The first paramedic to arrive felt a "threading pulse", he said, but when two others examined the man, "they could not find a pulse and subsequently declared the gentleman dead".
The pair had not been able to use monitoring equipment because it was difficult to reach the man, as he was trapped in the wreckage.
The emergency service controller at Bacchus Marsh, David Lambrick, said that the case was "extremely unusual".