Australia were both impressive and imperfect as they followed up their SailGP win in Auckland with some sizzling starts on day one of the latest event in Sydney Harbour.
The host nation won the third and fourth races on Saturday after finishing third in the opening race and second in the second.
They finished the day on 37 points, five clear of Great Britain, with France, competing in their first event of the year, another five points back on 27.
Switzerland (26), Denmark (24), Spain (21) and Canada (20) all remain in contention for a spot in the three-boat final, with either two or three more fleet races on Sunday before the decider, depending on weather conditions.
The Australians won the start in three of the four races, which the 11 F50 catamarans contested in winds of up to 30km/h.
"We've actually got plenty we can learn and sail better," Australia driver Tom Slingsby said.
"Even though we're getting good results, it's mainly coming from the starts.
"We're sailing well, but there's still plenty of mistakes."
Only 11 of the 12 nations competed, after the United States boat capsized on Friday and was forced out of the event with damage to their wing sail.
In Saturday's first race, France flew off the line but Switzerland finished first, a misjudgment from the Australians allowing the European boat to slip away and Spain to move past them into second.
In the second race, Australia shot away from the start and together with Great Britain contested the lead.
The British boat found a little more speed over the last couple of legs to win by four seconds from Australia, with France third, more than 20 seconds behind.
"Nice to get one over them (Australia) and show that we're here and we are a strong team," GB driver Dylan Fletcher told AAP.
"Happy to come away with a reasonably solid day," he added, after GB also recorded two thirds and a fifth
Australia led all the way to win race three from Switzerland, with GB third.
The home boat put on another clinic in the final race to cross the line ahead of France, with the British third.
France, who weren't able to contest the first two events while their boat was being built, recorded finishes of fourth, third, eighth and second, despite having only practised on the vessel for the first time on Friday.
"I truly believe this team is able to win this league and I think what they proved today is, even without any training or starting the season quite late, they can be competitive," France driver Quentin Delapierre told AAP.
It was another tough day on the water for New Zealand after they missed out on the final in their home event last month.
They finished last in each of the last two races, after eighth and seventh placings in the first two.
Driver Peter Burling revealed one of the boat's rudders wasn't working.
