The next day, at the start line, he noticed the pint-sized pooch next to him, its tail wagging. He waved it away, worried it might get trampled by the 100-strong field of runners as they made their way over the Tian Shan mountain range.
Still, the dog tagged along, following him across the mountains, through forest terrain and over a river crossing before ending at the finish line for the day’s stage hours later.
Dion remembered: "I started to speed off and I'm thinking, this dog won't last the whole day but she was still with me at the end. From then on she didn't leave my side."
The pair developed a close bond as 42-year-old Dion fed and watered her, even carrying her across rapids and risky terrain, and letting her sleep in his tent at night.
He and the dog, who he had already christened Gobi, went on to finish the seven-day race across the vast desert in China and Mongolia, and Dion decided he would take her home to Edinburgh, where he lives with his wife Lucja.
Dion, who finished second, said: “Seeing Gobi on the race changed my outlook on things. It made me think more about stopping and helping her, rather than just focus on winning. It also made my running more enjoyable. I thought: ‘If she could do it, so could I.’”
He left Gobi at the home of one of the race organisers in Urumqui, capital city of Xinjiang, and flew back to Edinburgh, where he started proceedings to bring Gobi home.
But just before she was due to travel to Beijing to enter quarantine, Gobi went missing in the sprawling metropolis of more than three million people.
Devastated Dion flew back to China to look for her, launching a media and social media campaign and putting posters up all over the city. Volunteers helped him scour Urumqi, asking security guards, taxi drivers, cleaners and fruit vendors, as well visiting parks and dog shelters to see if anyone had spotted Gobi.
Local television interviewed him, with one news outlet even keeping a live blog to update people about the search, but after a fruitless hunt over two weeks Dion was on the verge of giving up.
Then a local man spotted the stray dog in a local park while walking his own dog.
Dion remembered: "Gobi spotted me as soon as I walked in, and she started running toward me. Literally, she was running up my leg and jumping all over me and squealing with delight."
"It was just mind-blowing to think that we had found her. It was a miracle.
“Lots of Chinese people spoke about past life connections. When she went missing and we found her, I think that was double fate."
Refusing to let her out of his sight this time, Dion was given a sabbatical by his firm, a whisky distiller, and moved into a flat with Gobi in Beijing for four months.
Finally, in January this year, the two made it back to Edinburgh, where Gobi, who vets believe is a possible mix of pug, shih tzu and Chihuahua, now shares the bed with her adoptive parents and their nine-year-old cat Lara.
Dion's book about the adventure, Finding Gobi, has now been translated into 25 languages, while a Hollywood movie by 20th Century Fox is also in the making.
Dion said "Gobi continues to surprise and amaze me every day and she is a great voice for the Adopt Don't Shop message for rescue and shelter animals in need."
He said Gobi is unfazed by her new-found fame - her favourite activity is still running and she routinely does at least five miles a day with him over the Scottish hills.