Boyle won the 800m freestyle final after earlier finishing fourth in the final of the 200m freestyle.
She headed off Welsh swimmer Jaz Carlin, who beat her in last year's 800m freestyle final at the Commonwealth Games before Boyle reversed the result in the 400m freestyle in Glasgow.
Boyle, the world silver medallist, finished two and a half seconds clear of Carlin with Germany's Sarah Kohler third.
Boyle will compete in the 400m freestyle tomorrow before competing in the final World Cup meet in Dubai at the weekend.
She was the only New Zealand swimmer to qualify for finals on the first day of the two-day competition.