Hours after finishing a first aid training course, Nancy Ofanoa was giving CPR on the side of the road — saving a man's life.

Two weeks ago, Auckland resident Ofanoa, 28, was sober driving friends home after a night out when they came across the a car that had crashed into a power pole.

After scouring the scene in the dark, Ofanoa said she found the driver out of the vehicle and on a patch of grass alongside the road.

He "could hardly even take one or two breaths a minute", and emergency services were nowhere to be seen.

Having completed a first aid course through St John just the day before, her training kicked in.

"Something switched," she said. 

Ofanoa rolled the man onto his side, slightly opening his airway, and he began to splutter. 

While on the phone to 111, Ofanoa administered CPR until paramedics arrived and took him to hospital. 

The driver has since been discharged from hospital.

Ofanoa said it "shocked" her how calm she was. 

"I couldn't believe I had only just learned to do first aid and here I was actually performing CPR. It was such a coincidence. So lucky."

But St John's head of first aid training Julian Price said Ofanoa's reaction was the "ultimate result" of quality first aid training and exactly what St John aims to achieve.

"It just goes to show that you never know when you're going to need it.

"If she hadn't have reacted when and how she did the patient probably wouldn't have survived. Massive kudos to her," Price said.

Early first aid intervention can be life-saving - so where bystanders often stand back unequipped, it's better to do something than nothing, he said. 

Confident bystanders who have the right skills can literally save lives, Price said. 

"In Nancy's case, she's done the training then only a day later has the confidence and competence to put it into practise and save a life – what more could you ask for?"