There is a three minute artistic free routine, which they swam to a wolf-themed choreography, and Figures - four compulsory elements that all 242 competitors swim in a marathon seven hour session in the pool for both judges and swimmers.
Their Figures scores are then added together, averaged, and added to their routine score for a final score.
The duo's free routine placed 28th in the world with their combined Figures scores getting very close to climbing them a further place.
Both swimmers are building up some strong international experience having been two of the younger swimmers in the Aquaferns team that competed in the Spanish Open, Swiss Open and FINA World Champs last year.
As a duet they have competed in the Australian Open and recently placed second at the Oceania Championships in Fiji.
"I really enjoyed the whole experience," Eva said.
"To see the top athletes from Russia, China, Japan and Ukraine up close was a little bit terrifying to be honest, but also very inspiring. In those countries, synchro has a big profile - they're a bit like our All Blacks or Silver Ferns."
For Jazzlee Thomas the experience was also very positive.
"We now know how hard we will have to work to achieve our goals."
For both girls, hard work and juggling priorities is something they've become very good at. They fit 18-20 hours of training a week around their studies and work.
Jazzlee is a full-time Year 13 student at Bethlehem College, while former Tauranga Girls' College student Eva is now working and studying part-time through Te Kura.
That hard work will increase as they begin work on a four year programme with the goal of the Tokyo Olympics at the end.
Their next focus is to defend their Junior Duet title at the New Zealand National Championships which will be held at Baywave, Mount Maunganui, from September 25-27.