"It was a pretty weird conversation to have because I flunked maths at school and I was pretty mean to him (as a maths student)," explains Oska. "He said to me, 'I'll pick you up at 6am in the morning' and the next day we went running around the Port Hills. What that experience showed me was I was not the bee's knees as a runner, but that if I put my mind to it I could be good at it."
Encouraged by the possibilities of running and under Costley's measured guidance, Oska quickly made progress and shortly after taking up the sport struck gold at the Canterbury Schools' Championships for both cross country and on the road.
Some nine years later on from his introduction to the sport of running and Oska cuts a much more content and happy individual. Married with a seven-week-old child, and working as a manager in a thriving business the future looks rosy.
Yet perhaps none of this would have even been possible without running, which he says has "paved the way" for what the 25-year-old has accomplished in his life.
Born and raised in Christchurch, Oska always knew he had good natural endurance.
"I was never the most skilful footballer and I was never going to play for the All Whites, but it was my job to exhaust the guys who were playing left midfield and left back and then (when the opposition players were fatigued) I would run rings around them in the last 20 minutes."
Aged "13 or 14" the St Andrews College student was diagnosed with depression and his behaviour at school deteriorated. Struggling to focus in the classroom, he found salvation - thanks in large part to Costley - through running. It gave Oska a positive focus for his energies and the success proved motivating.
After enjoying some promising early results, Oska later further cemented that potential to finish 11th in the 2010 Melbourne Half-Marathon, aged 19, in a time of 1:12:40 before he and his then girlfriend and now wife, Katy, left Christchurch to set up a new life in Wanaka.
Coached by Val Burke and based in an idyllic training environment he continued to show flashes of his raw ability. In 2012 he was crowned New Zealand Half-Marathon champion in Palmerston North and the following year he further underlined his talent by securing top spot the Auckland Half-Marathon.
However, despite occasional successes, his four-year period in Wanaka was consistently sabotaged by injury- calf problems in particular derailing his development.
Returning to Christchurch with the aim to start a family, he sought a new coach and linked up with Matt Ingram, the man who guided 2014 national road and cross country champion Callan Moody and three-time New Zealand steeplechase champion Daniel Balchin. Oska instantly felt at ease with Matt and the New Zealand half-marathon champion believes his coach has been instrumental in bringing about the best form of his career.
Operating a less prescribed training programme than in the past, Oska has thrived under Ingram's direction which has given the Cantabrian a sense of ownership of his training.
"Matt always asks what I think I should be doing and what I think I should be working on," explains Oska. "It is not a dictatorship. He is very good at asking me the questions and getting the answers out of me. There are no written workouts on the back of my hand. There is no pressure at all. I have got the love and enjoyment factor back for my running."
Working full-time as the South Island Thirst Manager for SOS Rehydrate, he typically trains twice a day regularly racking up between 150 and 160km a week. Running some "big mileage" but with a focus on quality he carries out the bulk of training on his own - a fact which does not concern the New Brighton Olympic runner.
"I can absorb a good amount of training and I can do it alone," he explains. "The company is few and far between (for training) and I guess I can suffer for a long time without complaining too much."
He enjoyed what he describes as "a pretty good" first year under Matt's direction in 2015. In his first major cross country assault since high school, he earned a bronze medal at the New Zealand Cross Country Championships in Christchurch and also claimed an impressive win in the Wellington Half-Marathon, but two performances in particular convinced Oska he was on the right track.
"I ran the 10km in Christchurch in a PB of 30:21 but I felt I could have run even faster," he insists.
In October last year came further affirmation of his improving form when he took almost a minute-and-a-half from his half-marathon PB to place fourth in Melbourne in 1:05:57.
"I ran faster as the race went on," he adds of his Melbourne performance. "Fifteen kilometres into the race I was speeding up and I ran the last three kilometres in 8:45. If I had run another kilometre, I would have finished on the podium."
This year the good performances have continued. In March's New Zealand Track & Field Championships in Dunedin he earned a silver medal in the 5000m behind Hayden McLaren despite tearing a calf muscle in warm up before the race.
Then earlier this month he shrugged off the inconvenience of near freezing conditions and a mix-up at the end of the race in which the champion went off course in the dying embers of the race to regain his New Zealand Half-Marathon title from Aaron Pulford in 1:06:34 - the second fastest half-marathon time of his career.
With an ability "to hurt for a long-time" but accepting he does not have the natural speed to run a 61-minute half-marathon, Oska believes that his premier event is the marathon and he has tentatively pencilled in next February's Tokyo Marathon for his debut over the 42.2km distance.
Other potential options could be October's Auckland or Melbourne Marathons as he steps up his ambition to target a place on the New Zealand team for the marathon at the 2018 Commonwealth Games in Gold Coast.
Yet for Oska the bigger picture is less about his own personal running ambitions, it is more about how the sport has helped him overcome his personal challenges.
"I'm pretty good today," he says of his overall well-being. "You can't run away (from depression) but you can definitely learn to cope."
So where does the Cantabrian believe he would be without running?
"To put it in perspective, I probably wouldn't have finished school," explains Oska, whose first child, Indi, was born seven weeks ago. "I started the sport through Phil, and I believe everything happens for a reason. I then moved to Wanaka, I met a coach and that started a chain reaction, which has allowed other things to happen and I have made the most of those opportunities. I'm never going to be David Rudisha, but I think the most important thing is to be happy and content with what you are doing and to do the best that you can."
