An iron spike plunged fivecentimetres into his throat, narrowly missing his carotid artery, oesophagus, windpipe, all the major nerves in his neck and throat and just stopping short of his brain.
Doctors say the fall could have killed him instantly. Instead he was able to pull himself off the spike and scream for his mother, Priscilla Boswell, who was inside with her other child, eight-month-old Tom.
"It's really barbaric to get cut by a spike in your neck," Boswell said. "It's something from the dark ages.
"It's a horrible thing to think about.
"You just feel sick. I was holding Hugo on the ground and calling the ambulance with the phone in the other hand. I must have screamed and people walking past heard me."
Passers-by rushed into the house.
They wrapped Hugo in a clean towel following directions given by paramedics to Boswell over the phone.
Hugo's father, Peter Borbilas, ran from the cafe he owns at the end of the street as the boy was rushed to Royal Prince Alfred Hospital.
After an initial examination and scans, the parents suffered an agonising five-hour wait before their son was transferred to Sydney Children's Hospital, Randwick, for emergency surgery.
Doctors warned the family Hugo might have brain damage or spinal injury and could suffer stroke, intestinal infection and eye problems.
"I could put my index finger in the wound right through to the knuckle," pediatric surgeon Vincent Varjavandi said last week.
"It ran up towards his brain but just fell short. It went between everything: his windpipe, his oesophagus ... Cutting any of those could have proved fatal either in the bleeding at the scene or in the hours afterwards," Dr Varjavandi said.
"Penetrating neck injuries are extremely rare in kids. They're usually seen in adults who receive them through assaults. And where Hugo was impaled is the most dangerous zone. It was virgin territory for me."
Hugo underwent a 90-minute operation to explore possible damage in the wound and clean it.
Remarkably, though one of the main arteries in his neck has been permanently blocked by the puncture, he has suffered no other lasting damage.
"I was lucky because I didn't pierce [the artery], but it hurted a lot," he said.
Hugo will appear in a forthcoming episode of the hospital reality television series RPA.
Ms Boswell said she had no plans to take down the fence, although her sons would no longer be allowed in the front yard alone.