Brazil's Olympic champions Martine Grael and Kahena Kunze started in style at the Sailing World Cup in Enoshima, winning both of their races in the 49erFX class.
The Rio 2016 gold medallists are looking for a second consecutive win on the Tokyo 2020 Olympic course after triumphing in the test event for the Games last week.
They also won the Enoshima World Cup last year, and on this evidence will take some stopping again.
"It changes so much here because one day there's a sea breeze and the next it's coming from the shore so you have to be adaptable to be successful," said Kunze.
The Brazilians have two points on top of the leaderboard, with Spain's Carla and Marta Munté Carrasco and Singapore's Kimberly Lim and Cecilia Low tied on eight.
Enoshima is the first stop on this year's World Cup circuit with athletes due to battle throughout the season to prove their Tokyo 2020 credentials.
Varying wind conditions meant not all of the fleets could complete their scheduled races with any action missed now added to tomorrow's programme.
In the men's 49er Tim Fischer and Fabian Graf of Germany were the only crew to achieve three finishes within the top 10, giving them a share of the lead on six points with Dominik Buksak and Szymon Wierzbicki of Poland.
The men's laser is headed by Croatia's Tonci Stipanovic on eight points after two races, while Japan's Manami Doi has the same tally to sit at the summit of the women's laser radial standings on home water.
Doi is only two points in front of Belgium's test event winner Emma Plasschaert who claimed a race win en-route to a score of 10.
For the 470 fleets this is the third consecutive event on the Olympic course after their World Championships were also held there earlier this month.
Only one race was possible in the men's and women's classes, with Yuki Hayashi and Chika Nishidai winning the latter for hosts Japan to top the charts.
Paul Snow-Hansen and Daniel Willcox of New Zealand won the men's race to position themselves as the early leaders.
Britain's Ben Saxton and Nicola Boniface top the pile in the mixed Nacra 17 class with five points from two races, including a victory.
In the day's only finn race, Croatian Josip Olujic crossed the line first.
Light breezes made windsurfing difficult but three races were held in both fleets.
Spain's Angel Granda-Roque recorded finishes of first and second to lead the men's RS:X charts on three points as Peina Chen of China did likewise to take control of the women's RS:X competition.
Action is due to continue tomorrow but organisers are wary of forecasted strong winds.
Competition in Enoshima will continue until Sunday (September 1).