Ukraine's Yana Klochkova confirmed her position as the world's best all-round female swimmer when she became the first woman to retain the Olympic 400 metres individual medley title on Saturday.

The 22-year-old fought off a great challenge from American Kaitlin Sandeno to win gold in a time of four minutes 34.83 seconds, just outside the world record of 4:33.59 she set in winning her first Olympic title in Sydney.

Klochkova was pushed all the way by Sandeno who took the silver in 4:34.95. Georgina Bardach of Argentina getting the bronze in 4:37.51.

Katie Hoff of the United States, ranked number one in the world heading into the Olympics, failed to reach the final after finishing 17th in the morning heats.

Hungarian Eva Risztov, runner-up at last year's world title, led the race after the opening butterfly leg but Klochkova surged ahead after the backstroke.

She was still in front at the end of the breaststroke but Sandeno snuck past her turning for home, setting the scene for a gruelling last lap.

Sandeno was still ahead halfway down the final length but Klochkova, who also won a 400 freestyle world title in 2001, reeled her in to get to the wall first.

Klochkova has been virtually unbeatable over the past five years and is hoping to repeat the 200-400 medley double she completed in Sydney four years ago.

Trained by Nina Kozuch in Kharkov, Klochkova also has a stack of world and European titles to her credit and is already eying a third Olympics in Beijing.

Only two swimmers, Australia's Dawn Fraser and Hungary's Krisztina Egerszegi, have won the same event at three Olympics.