Grainger and Watkins took five seconds off the Olympic record as they qualified for the final of the women’s double scull at Eton Dorney, taking the heat in 6min 44.33sec.
After winning three silver medals in previous Olympics, Grainger will be going for gold in London 2012.
The GB boat was in front of the race from start to finish, leaving New Zealand and China in its wake.
In the other heat, main rivals Australia took four seconds longer to finish the race. The Aussie team, Kim Crow and Brooke Patley will also be chasing the gold, although Crow also took on the women’s single scull on Saturday.
Britain’s Watkins has expressed her surprise that Crow would take on two events but the Australian hopeful laughed off her comments, saying:
“Back in Australia we will race three races in a morning.
“It is not ideal but it is something we are trained to do. It is pretty interesting. From the people inside the Australian camp I don’t know anyone who thinks it is a bad idea. I think it is a great idea. I am loving it.”