Lizzie Armitstead has won Team GB's first medal of the London Olympics after coming second in the women's road cycle race.
Armitstead was beaten in a tight finish in the Mall by Marianne Vos of the Netherlands. Russia's Olga Zabelinskaya was third.
Nicole Cooke, the champion four years ago in Beijing, finished some way behind the leaders in the main peloton.
Armitstead, Cooke and fellow Brit Emma Pooley were hoping to make up for Mark Cavendish's shock defeat in the men's road race yesterday.
Earlier swimmer Rebecca Adlington started her Olympic campaign with the defence of her 400m freestyle title - the first of three events in which she is competing.
Adlington, who also won 800m gold in Beijing, qualified for the 400m final tonight in eighth place.
There was not such good news from Paula Radcliffe, however. She has dropped out of the women's marathon after a foot problem fkared up again.
Earlier Radcliffe, 38, tweeted: "Not looking good but my heartbreaking news to break!", adding she would not make a decision until a final training run.
Games organisers were hoping the hundreds of empty seats at the Aquatics Centre and other Olympic venues yesterday will be filled today.
Locog has launched an investigation , while the Government has expressed concern as to why the seats were not taken despite events being apparently sold out.
Elsewhere, triple Olympic sailing champion Ben Ainslie has begun his quest for another crown, while rowers Zac Purchase and Mark Hunter were starting the defence of their lightweight double sculls title.
Andy Murray was also due to be in action in the tennis at Wimbledon; Team GB's men's football team will take on the United Arab Emirates at Wembley stadium this evening.
They will be hoping to emulate the women's team who secured a quarter final place last night with a 3-0 win over Cameroon.