Great Britain's Helen Glover and Heather Stanning set a new Olympic record with a dominant victory in the first heat of the women's pair.
The duo, who won gold in all three World Cups this season, clocked a time of six minutes 57.29 seconds.
They romped home by a length from the United States with both pairs progressing to Wednesday's final.
Britain's men's eight came second to Germany in their heat, and must contest the repechage to make the final.
Stanning and Glover have been unbeaten since taking silver in the World Championships last year behind New Zealand.
At a sunny Eton Dorney, the duo employed their usual tactic of going out hard, moving one second clear of the field after the first 500m.
They then eased off and controlled the race in front of packed grandstands to finish ahead of the US, Olympic champions Romania, Germany and Argentina.
Glover said: "Plan A is always to expect to race to the line, and plan B is to conserve what we can. In the last 500m we rowed like how we felt we wanted to row.
"We are going to sit with our feet up today, and in the next couple of days we'll keep ticking over by doing some training, and the final will be the peak of our season."
In the other women's pair heat, Australian duo Kate Hornsey and Sarah Tait eased to victory over world champions New Zealand, with both duos progressing to the final.
Britain's men's eight were racing with their current crew for the first time this season with Constantine Louloudis, recovered from a back injury, alongside Alex Partridge, James Foad, Tom Ransley, Ric Egington, Moe Sbihi, Greg Searle, Matt Langridge and cox Phelan Hill.
World champions Germany went out hard to lead by a length at 1,000m - the halfway point - but Britain responded well, with Louloudis upping the stroke rate.
But it was not enough, with the home favourites closing to within half a length and crossing the line second in a time of five minutes 27.61 seconds, with only the winners qualifying directly for the final.
Hill told BBC Sport: "If we are honest, we are not where we want to be yet.
"The Germans are the stand-out crew, but today was the first race in our full line-up in the correct positions - we have something to build on.
"At the moment, we need to improve on our first 500m. We have to be closer to the Germans to stand a chance.
"We need to dig a little deeper and commit ourselves a bit more. I think the crowd make a massive difference so hopefully that will do us some favours."
The US won the other men's eight heat to go straight into Wednesday's final.
The British men's lightweight four - Peter Chambers, Richard Chambers, Rob Williams and Chris Bartley - produced a fightback to overhaul world champions Australia and take victory in the heats to progress to the semi-finals.
"That's gold medal pace," said BBC Sport summariser and ex-Oxford coach Dan Topolski. "They've still got to get to the final, but they showed that they have what it takes to take on Australia. That was very, very impressive."
Britons Bill Lucas and Sam Townsend, who are in their first season together in the double after moving from the quad, gave the crowd a grandstand finish. They just missed out on victory to New Zealand but second was enough to progress to the semi-finals.
The British men's quadruple scullers - Stephen Rowbotham, Tom Solesbury, Charles Cousins and Matt Wells - finished a length behind world silver medallists Germany but still progressed to the semi-finals.
Britain's men's pair George Nash and Will Satch are through to the semi-finals with a gutsy victory in the third heat after New Zealand duo Eric Murray and Hamish Bond benefited from a tailwind to beat Sir Matthew Pinsent and James Cracknell's 10-year-old world record by six seconds in an earlier heat.
Alan Campbell looked very comfortable as the Briton sealed his place in the men's single scull quarter-finals with victory in heat five.
But it was a disappointing performance from the British women's quad, who were silver medallists in Beijing.
Mel Wilson, Debbie Flood, Frances Houghton and Beth Rodford trailed home fourth behind winners Ukraine and must now contest the repechage.