As the bounding deer landed in the open-topped sports car, its hooves smashed into Willie's ribcage and sent the vehicle hurtling out of control - straight into a tree.
The freak countryside accident saw the fibreglass kit car disintegrate on impact and Willie left fighting for his life with multiple critical injuries.
As firefighters, ambulance crew, police and a specialist trauma team battled to save Willie at the roadside, Scotland's Charity Air Ambulance was scrambled in a desperate bid to get the injured driver to life-saving hospital care in time.
"The deer came out of nowhere," recalled Willie, an agricultural fencing contractor well used to driving Scotland's rural roads. "There was nothing I could do.
"I remember the crushing pain as the animal landed on me and remember hitting the banking and flying towards the tree. Then I just drifted in and out of consciousness in a world of pain - pain like I've never experienced before.
"I remember hearing sirens, soft voices and questions I couldn't respond to. Then it all went black."
Willie woke up 65 days later in Ninewells Hospital.
"Doctors and family told me how my life had been literally ebbing away at the roadside," he said. "I was given multiple transfusions by Tayside Trauma Team but they couldn't fully staunch the bleeding. If SCAA hadn't airlifted me in time I could have bled to death at the scene."
Willie spent four months in hospital being "rebuilt", with multiple operations to piece his broken body together again with plates, bolts and grafts.
"Every part of me was crushed, broken or damaged - from my collar bone to my ankles," said Willie. "I couldn't even lift a spoon to my mouth and I had to learn to walk again.
"There were days I thought about just giving up and then I thought of SCAA and all the others at the scene and in the hospital who had battled so hard to save me and knew I had to fight on for them."
Three years on, Willie still walks with a limp and finds certain tasks too demanding or painful to undertake.
"But I'm alive," he said. "My family have their husband, father and grandfather back."
Willie says he owes his life to so many people who played a crucial role that day - but he's in no doubt the life or death race against time was won for him by SCAA.
"SCAA helped save my life when every second counted," he said. "No one expected me to make it to hospital alive - I was dying. But SCAA's speed, expertise, efficiency and professionalism ensured I had the best fighting chance possible.
"I'd seen SCAA in action at an accident scene before and witnessed what a slick and professional outfit it is. It's only when you are on the receiving end of their care, however, that you realise what a vital lifeline the charity air ambulance is in Scotland.
"I can never thank them enough. I wouldn't have made it without them."