Johnston and Markby broke away from the bunch early but then had a nasty fish fall - although not as bad as Johnston's accident in training for the event three years ago which put him in hospital in a neck brace and with massive grazes after he was knocked off his bike by a motorist.
"I just ran it too hot around a corner and hit the deck, and took out Matt, and then everyone went past us.
"We kind of just brushed ourselves off and got back on, then caught the front guys up again and drifted them off one by one," Johnston casually explained, adding they were tired after a week's worth of 190km rides as part of the Tour of Southland - where Johnston finished 14th.
While Sunday's win was satisfying, it's just the beginning for the 18-year-old who is soon to be an international rider.
"Next year is pretty much where it all starts, under-23. I'm looking to go to France, I already have a team sorted but might do something [professionally] in New Zealand or Aussie first."
Currently Johnston is based in Christchurch where he works for cycling company Chain Reaction Cycles Specialized and cycles with the Benchmark Homes Cycling Team.
Sunday's Memorial Ride included a 12.5km family fun ride, named for Whangarei businessman and keen cyclist Michael Springford, which was won by Jack Gascoigne.