It was an even race at that point, with the Beijing Olympic Games crew of Storm Uru and Peter Taylor sharing the lead with Cohen and Trott.
The strong easterly wind roughened up the lake surface, which proved the undoing of Uru and Taylor (Southern Regional Performance Centre).
Uru (23), who won a gold medal at the world under-23 world championships in 2006, caught a wave and his oar lock was mangled and twisted.
When the crew stopped to get the oars back in working order, Cohen and Trott pulled away to win the race.
Trott and Cohen won by 5.63sec from the Central RPC combination of Steve Cottle and Joseph Sullivan.
The bonus went to the Southern RPC third team of John Storey (Avon) and Michael Nisbet (North end), who won their first premier title.
Cohen (23) rowed in the double sculls with Rob Waddell at the Beijing Olympics and has also won silver medals at the world under-19, under-21 and under-23 world championships.
It was the fourth red coat for Cohen, who started rowing in Invercargill and had one year studying accounting and economics at the University of Otago before being called into the Rowing New Zealand high-performance squad.
"It was rough out there," Cohen said. "We just concentrated on keeping out of trouble. That is what the best crews do."
It was a significant achievement for Storey and Nisbet to stand on the podium in a premier event.
The Royce Wilson-coached crew put their act together when training on Otago Harbour and on the Taieri River during Waitangi weekend.
Nisbet (21), an apprentice carpenter, started rowing at Kings High School and was the Otago rower of the year in 2007 after winning the national single and double sculls titles.
North End's Hamish Bond won his fifth red coat when he teamed with Jade Uru to convincingly win the men's premier pair by 4.10sec from Waikato's Eric Murray and Simon Watson.
Their sprint over the last 300m demonstrated the superior strength that Bond and Uru have over their opponents.
The Auckland RPC crew of Tamsin Gilbert and Emma Twigg were equally convincing when they won the women's premier double sculls by 5.10sec in 6min 56.53sec from the Central RPC crew of Anna Reymer and Simone Hudson.
Hudson is a former member of the North End club in Dunedin.
Former world champion Duncan Grant (Central RPC) dominated the men's lightweight single sculls and beat fellow international Graham Oberlin-Brown (Waikato RPC) by 6.12sec in 7min 04.27sec
