The pair returned from the recent age-group nationals in Cambridge with a gold medal each.
Harris won the women's under-23 72km road race while Milburn toughed it out for just under 26km to win the men's under-23 time trial by a mere 2sec.
Wanaka's Phoebe Young is another to watch. She claimed gold in the women's under-19 16.4km time trial.
Harris (18) finished third in the under-19 road race at the nationals last year, so she was thrilled to go two places better in a higher grade.
And to put her effort in further perspective, the under-23 riders raced in a group which included the senior women.
Harris was actually the fourth rider across the line and 1sec behind the women's winner Elyse Fraser, who had broken away with 1.5km remaining and held on by a narrow margin.
The peloton had broken up by the time the race entered its final stages.
Harris had a quick look around and realised she was one of three under-23 riders left in the leading bunch.
''I was guaranteed a medal but I just knew I had to nail the sprint finish which is not normally my strong point,'' she said.
''I ended up getting on someone's wheel and sprinted around them at the end, so it worked pretty well.''
Harris hopes to race overseas in the future. She went to Australia last year and enjoyed the experience.
She would also love to represent her country at under-23 level and continue to improve as a rider.
Milburn was hoping to do well at the nationals but his win still came as a surprise.
He made the switch from BMX to road cycling 18 months ago and his time of 33min 15sec was just good enough to edge Auckland's Logan Griffin.
''I was expecting to do well but I was on a borrowed bike ... and I hadn't really trained on it,'' Milburn said.
''I'd been training on my road bike so I was in a completely different position.''
The final results took time to be processed and Milburn actually got the news from Harris, who yelled across the road ''Hey, Will. You won''.
Milburn switched to road cycling for something different and also the ''massive jumps'' meant really committing and ''it wasn't really for me'', he said.
''I always liked going fast and training hard and that is where road cycling is good, because that is what you do. It is not quite as technical.''
Milburn moved to Dunedin about 10 months ago from Tauranga and his next events are the last three rounds of the Calder Stewart Cycling Series which resumes in September.
He is fourth in the under-23 classification and 10th overall. Following that, he hopes to compete in his first Tour of Southland and the elite nationals in January.
Two other Otago riders collected medals at the age-group nationals. Sarah Saunderson-Warner was third in the masters 1 time trial, and Geoff Keogh was second in the masters 4 road race.
