Mr Cuthbert was flung from the vehicle before it flipped, spun several times and landed on his abdomen, pushing his organs upwards and preventing him from breathing. He also had severe head injuries and died at the scene.
The accused was found to be about two and a half times the legal breath alcohol limit and arrested, despite claiming Mr Cuthbert was the one driving.
No one witnessed the crash, but prosecutor Brett Tantrum said the Crown would produce expert evidence showing that Watson must have been the driver.
A professor of physics had created an animation simulating the crash which determined this to be the case, he said.
Mr Cuthbert's family members had seen Watson driving Mr Cuthbert's ute before.
It was not in dispute that the ute was being driven dangerously -- about 95km/h in a 50km/h zone -- nor that Watson was disqualified from driving and drunk.
"The sole issue is for you to determine is who was driving," Mr Tantrum told the jury.
Watson's lawyer John Cagney said the defence would call its own well-qualified expert who had come to a different conclusion about who was behind the wheel.
"That's what it's about: who was driving and does the evidence establish who was driving or is there still a reasonable doubt?"
The trial, before Justice Patrick Keane and a jury of eight men and four women, is expected to take between three and five days.
- NZPA