Christie-Johnston has had a hand in advancing the careers of World Tour riders Richie Porte, Nathan Haas, Campbell Flakemore and new Greenedge recruit Jack Haig - but Cooper's career was derailed in 2014 when he broke a pelvis during an Australian National Road Series race, where he has twice been champion.
"This is the icing on my whole season," Cooper said after yesterday's race.
"To win an HC race in the New Zealand champs jersey, that's just such a special thing for me. I've worked hard all year and this being my best season to date, hopefully I'm not done yet."
In the stage, Cooper attacked with about 14km to go and held off the bunch behind to take victory.
Italy's Jacopo Mosca (Wilier Triestina) held on for a narrow overall victory at the Tour of Hainan. The 24-year-old concluding the nine-stage Chinese race three seconds clear of Benjamin Prades (UKYO) and five seconds up on Emils Liepins (Delko Marseille Provence KTM).