David Rudisha won his first Olympic gold medal with the kind of world-record performance that has made him almost unbeatable the last three years.
The 23-year-old Kenyan won Thursday's final in 1 minute, 40.91 seconds, shaving one-tenth of a second off the mark he set in 2010, and setting the first world record on the track at the London Olympics.
After crossing the line, he flung up both arms to celebrate, then draped himself in a national flag and posed for photographs near the timing clock with ''NEW WR'' on it.
Nigel Amos of Botswana, the world junior champion, took silver in a national record 1:41.73 and Timothy Kitum of Kenya got the bronze in 1:42.53.
Americans Duane Solomon and Nick Symmonds finished fourth and fifth, just ahead of 18-year-old Mohamed Aman of Ethiopia, the world indoor champion who handed Rudisha his only loss since 2009 last September.
Sebastian Coe, a middle-distance running great and head of the London organizing committee, described Rudisha's win as one of the greatest in the Olympics.
''That was simply an unbelievable performance,'' Coe said. ''David Rudisha showed supreme physical and mental confidence to run like that in an Olympic final.
''Instead of just doing enough to win the race, he wanted to do something extraordinary and go for the world record as well. Rudisha's run will go down in history as one of the greatest Olympic victories.''
Kitum, who finished more than 1 1/2 seconds behind his fellow Kenyan, said Rudisha had warned other runners to be prepared for something special.
''Yes, he's the greatest runner,'' Kitum said. ''He told me he's going to run a world record today. He's the best.''