The 20-year-old on Wednesday finished the first stage of the New Zealand Cycle Classic, a five-day 2.2-ranked race. He finished 64th.
On June 5, 2016, he was feared dead after crashing into the rear windscreen of the Dimension Data for Qhubeka team car.
"I'm 100 per cent [it's a miracle]! I think that day everything went 'perfectly,' given the situation. If only something had gone differently, today I would not be alive," he told La Gazzetta dello Sport.
Referring to racing in the Tour de France, he added, "The goals are always the same. Nothing has changed."
Girdlestone returned to race with New Zealand team, Frezzor Racing after a year of intense rehabilitation and training.
"I'm in the best shape I've ever had since the accident," he added. "Clearly, I have no great expectations, just a list of goals that I will check off during the tour as I reach them: finish in group, then finish in the first 20, then try to attack, then finish on the podium, then... I am an opportunist: if there's a chance to get the result and my legs are fine, I'll try."
The competitive spirit saw him place fourth in the junior world championship time trial in 2015 and sign to ride for Dimension Data's continental team.
Racing with the team in the under 23 race Coppa della Pace, he fell around 105 kilometres and hurried to rejoin the group when the incident occurred.
He spent 10 days in a coma and three weeks in intensive care. Curing the injuries, not racing was top priority as messages of support poured in from many including Chris Froome. Edvald Boasson Hagen dedicated his Critérium du Dauphiné stage win to Girdlestone.
"Of the crash I only remember the sensation of a hot liquid, of blood, running over my neck and a spectator who shouted, 'easy, easy.'
"In intensive care, I remember a great pain, but also that I said to my parents, 'I will return to my bike!'" he continued.
He lost almost four litres of blood and passed two and a half hours without oxygen going to his brain. After surviving and returning home, it took him six months before he even rode his bike outside again.
"It taught me that if you believe in yourself, you work hard and do not let yourself be influenced by the opinions of others, you can achieve everything you want," he said.
"I hope that my story can instil hope in people. I had many idols in cycling that turned out to be scammers: it is demeaning.
"So I hope to be the change in our sport that I've always wanted to see: the human body and the mind are able to achieve incredible things on their own."
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