Helen Glover and Heather Stanning confirmed their status as gold medal favourites as they stormed into the final of the women's 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.
Saturday'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.
'It was definitely a heats race for us,' Stanning said.
“It was a solid performance. We felt quite controlled in our boat.
'We have a final to come and that is where we will pull out all the stops. The fact we've got all the people cheering for us gives you a surge, it makes you sit up tall and be proud to be representing them.'
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.
For Greg Searle, making his Olympic comeback at the age of 40 and two decades after winning gold in Barcelona, it was an emotional experience.
'It felt amazing. I did feel a range of emotions from excitement to feeling I was going to be sick with nerves as we rowed up to the start,' he said.
'It was definitely worth coming back, although this is clearly just step one and we still need to make the Olympic final.
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.
The British men's lightweight four of Peter Chambers, Richard Chambers, Rob Williams and Chris Bartley produced a barnstorming finish to beat world champions Australia and reach the semi-finals.
There was barely anything in it at the 1500-metre mark but the British crew pulled clear to win by a length and set out their gold medal credentials.
'We have come here knowing we can do it,' Richard Chambers said.
'We just have to deliver it now. We did that today. We have two more races to go out and win.'
The men's pair of George Nash and Will Satch were also victorious to reach the semi-finals – but their achievement was overshadowed by New Zealand's Hamish Murray and Eric Bond smashing the world's best time in the other heat.
Richard Chambers and Chris Bartley
Murray and Bond won in six minutes and 08.50 seconds – almost six seconds better than the previous best, set by Matthew Pinsent and James Cracknell at the 2002 world championships in Seville, Spain.
The Kiwi pair are unbeaten since teaming up in 2009 and one of the strongest gold medal favourites of the regatta.
Britain's men's double of Bill Lucas and Sam Townsend reached the semi-finals with a second place finish behind New Zealand, who were pushed into setting a new Olympic best time.
'That gives us a good platform to build on,' Lucas said.
'It has been a long build-up to the Olympics and for us you want to get out there, put in a performance which shows you are in the right ball park.
'It would have been great to come out on the right side of the tussle with New Zealand but we have improvements we can make.'
The British men's quad of Stephen Rowbotham, Tom Solesbury, Charles Cousins and Matt Wells also qualified for the semi-finals in second place after finishing a length behind Germany.
Alan Campbell rounded off Britain's interest in the opening day of the regatta by comfortably winning his heat from China's Liang Zhang to reach the quarter-finals in a packed field.
The only real disappointment on the opening day was the women's quad, who trailed home last in their heat and must now negotiate a repechage to reach the final.