Helen Glover and Heather Stanning confirmed their status as gold medal favourites as they stormed into the final of the women's rowing pair in a new Olympic record time.
Roared on by a packed crowd at Eton Dorney, Glover and Stanning won the opening heat of the Olympic regatta in a time of six minutes and 57.29 seconds, beating the previous best by over four seconds.
Glover and Stanning controlled the race from the outset, leading the field by a half a length at the 500 metre time-check before pulling smoothly clear to beat the United States crew by a length.
The defending Olympic champions Romania came a surprise third and will have to negotiate the repechages to reach Wednesday's final.
Glover and Stanning reacted to being pipped into silver place at the 2011 World Championships by dominating the women's pair this year, winning gold at all three of this summer's World Cup regattas.
If they can continue that run of success into Wednesday's final they will become Britain's first ever female Olympic rowing champions.
Today's performance sent out a powerful message of intent to the rest of the field, with heat two winners Australia coming home in a time four seconds slower than the British crew.
New Zealand, who beat Glover and Stanning by eight hundredths of a second to win the World Championships last year, trailed home unconvincingly behind the Australians.
Great Britain's men's eight finished second in their heat behind three-time world champions Germany and will have to go through a repechage on Monday to reach Wednesday's final.
But racing for the first time with their current crew - with 20-year-old Constantine Louloudis at stroke after returning from injury - Britain produced a confidence-boosting performance.
Germany seemed in control at the halfway mark but Louloudis, the Old Etonian rowing on his school lake, inspired a powerful second 1,000 metres as Britain closed the gap to half a length.
The repechage will give Britain an extra race together. They should enter Wednesday's final with podium potential and, following today's performance, gold medal aspirations.
The race was five seconds faster than the first heat which was won by a resurgent United States crew, who had finished eighth at the World Championships and only qualified for the Olympics at the last opportunity.
Earlier, the British women's quad of Melanie Wilson, Debbie Flood, Frances Houghton and Beth Rodford finished a disappointing fourth in their heat and must now negotiate a repechage to reach the final.