Russia's Natalia Ishchenko and Svetlana Romashina won duet Olympic gold with a stunning display in the synchronised swimming final.
The pair, who won gold in the team event in Beijing, led after the technical round on Monday and totalled 197.100 after their freestyle routine.
Spain finished ahead of 2008 runners-up China in the battle for silver, while Great Britain were ninth.
"It felt like a good swim. We enjoyed the final," said GB's Olivia Federici.
The British duet scored 177.270 to finish ahead of France, the United States and Korea in the 12-strong final.
"In Beijing we didn't make the final, so it was great to make it this time and hopefully for the next Olympics we'll be even higher," said Jenna Randall.
The pair will return on Thursday for the first round of the synchronised swimming team event, which will be the first time Great Britain has ever competed in both disciplines at an Olympics.
The sport became part of the Olympic programme in 1984, but was dropped for the Atlanta Games in 1996.
It was reinstated four years later in Sydney, and a Russia pair has won the duet event in each Olympics since then.