He broke Donovan Bailey's world record of 9.84 seconds in 1999, setting a new mark of 9.79 which still stands. He followed that milestone with a second world championship 100 metres gold in Athens two months later and added the 200 metres crown to his haul to become the first man to win both events at the same world championships. Olympic gold followed in Sydney in 2000, when Greene won the 100 metres and then led the United States team to victory in the 4x100 metres relay.

Underlined his billing as the "world's fastest human" in 2001 after sweeping aside his rivals at the world championships in Edmonton, Canada. Matched the achievement of compatriot Carl Lewis as he collected his third world title over 100 metres, clocking the third-fastest time in history with 9.82 seconds, despite straining his left leg muscles with 30 metres of the race remaining. Led his team mates Tim Montgomery and Bernard Williams to the first 100 metres clean sweep at a major championship since 1991, but his injury denied him the chance to defend his 200 metres crown.