Vidal and Sissons swam well, exiting the water in a lead group of eight athletes which included another race favourite in Tony Dodds from Wanaka.
However, disaster struck for Dodds at the first lap turn when he crashed with another competitor, ending his race before it had really got under way.
Vidal and Sissons rode on with International Triathlon Union athlete Ben Shaw, and the three began to dominate on the tight and technical course in beautiful conditions.
Initially on the run it looked like Sissons and Shaw might have too much pace for Vidal, but the world number six found his rhythm and took the lead near the end of the first lap of two before running clear to secure victory.
"I raced here in 2009 ... but from what I remember it was a hard race and today proved that, it was a tough bike.
"The swim was crucial to set up for the bike, we kept pushing on the bike and they started so quick on the run I fell off the pace a bit but I caught Ryan and I think maybe I had a little more strength than Ryan on the run. Everyone had a good day today, though it is always tough to beat the Kiwis at home."
In the women's race McIlroy emerged from the water in a lead group of four but quickly went to work on the testing bike course.
Midway through, Auckland's Sophie Corbidge was the only athlete to be anywhere near the London Olympian.
"I wanted to bike hard, there wasn't as many girls with me," McIlroy said.
"Sophie rode really well - she stayed with me for a few laps and it would have been nice to have some company for the last few laps but I wanted to keep going, see what I could do and see how I could run off it.
"The lead happened naturally, when you are by yourself you can descend and corner quicker and make some time on the corners, but I just wanted to bike solid and run as well as I could so I am really happy with that.
Athletes enjoyed stunning conditions throughout the day, with age group titles decided earlier in the day.
The Erin Baker standard distance race got things under way on Saturday with a popular winner in the women's event - former world champion Sam Warriner.
