Ferguson is now regarded as one of New Zealand's fastest female iron-distance athletes, after a meteoric rise in the gruelling sport since 2006.
She put in a compelling performance at Challenge Roth in Germany last year, where she was third in 8hr 57min, and was eighth at October's World Championships at Kona, Hawaii, ahead of New Zealand's reigning women's champion Jo Lawn, who finished in 14th place.
Johnston told the Otago Daily Times yesterday she rated Ferguson and her other main rival, Hillary Biscay of the United States, as "top of top class" and "exceptionally talented athletes".
"I still have to pinch myself that I am on a start list with them because it's never where I imagined I would be," Johnston said.
But Wanaka fans can rest assured that Johnston hasn't thrown her race away and will be racing hard.
Although there are just three professional women athletes in the race, Saturday will be a pay-day for Johnston only if she can stay within a 7.5% cut-off time of her rivals, which she has estimated may be a gap of just 40min.
Johnston's second year as a professional athlete has been successful, winning her age-group at Challenge Roth and in New Zealand races.
Wanaka coach Val Burke is happy with her charge's preparation and believes she has evolved significantly since last year.
Although the women's professional field was small, elite athletes entered only if they thought they had a chance of winning, Burke said.
The Wanaka course was challenging in its terrain and environment and people interested in times should realise it was not a fast course, Burke said.
"I always like to see people do better than what they have done in the past. For me, it's about people reaching their potential," she said.
Johnston is happy with her physical shape and recent rehabilitation work on her calves. Her biggest struggle had been with the mental and emotional game.
"It has been more of a yo-yo year this build-up since I came back from Europe. I've had to spend a lot more time on head space, positive imagery, positive self-talk and I've had to lean on Val a number of times to learn a different view of where I am at," she said.
Johnston's husband, Mike, a triathlete and adventure racer, had also been a pillar of support.
Another highlight of last year had been the formation of Burke's growing stable of swimmers, cyclists and runners in Wanaka.
The group now numbers about 20 regular athletes.
Merryn Johnston
Fact file
Age: 31
Lives: Wanaka
Occupation: professional triathlete and part-time retail assistant
2008 race results: 4th Challenge Wanaka (10hr 36min); 15th Challenge Roth (9hr 52min); 1st Cromwell half-marathon; 1st Ashburton Half Ironman (SI Championships); 2nd Taupo Half Ironman
Coach: Val Burke
