Conditions in the Dutch city forced organisers to stage all heats in the time trial format, where boats raced against the clock and went one at a time at 30-second intervals.

The Croatian brothers, who missed the last World Cup in Poland owing to Valent's back problems, posted a time of 6min 46sec to progress to the next round.

It was not quite the fastest in the competition, however, as Thomas Murray and Michael Brake of New Zealand clocked 6:41.00 in the third heat.

Lukas Helesic and Jakub Podrazil of the Czech Republic were also quicker than the world champions, crossing in 6:45.00

The Dutch crew of Melvin Twellaar and Stef Broenink were fastest in the men's double sculls as they stopped the clock at 6:27.

Australia’s Georgia Newbitt and Germany’s Marie-Louise Draeger were the two fastest boats in the first heat of the women's single sculls competition.

Newbitt, considered among the pre-event favourites, completed the course in 8:14.00, while 38-year-old Draeger clocked 8:21.

The regatta, the last major competition before the World Championships, continues tomorrow.