The double Olympic champion, rocking with the effort in the final 10 metres, recorded a time of 44.31sec nearly a second slower than his best, to hold off his American rival Tyree Washington who recorded 44.38sec.
Davis Kamoga, of Uganda, the world's silver medallist was third in 44.43, with Britain's Roger Black, making his first individual appearance since returning from the virus infection which denied him an individual place in Athens fourth in 45.07 sec.
The crowd chanted Johnson's name afterwards, but for all his broad smiles it was a faintly desperate performance which underlined doubts about whether he has fully recovered from the injury that caused him to miss the US trials.
Colin Jackson, a surprise silver medallist at last week's World Championships, was unable to close the gap here on the man who beat him in Athens, Allen Johnson. The American won the Weltklasse Meeting 110m hurdles in 13.13sec, with Jackson back in fourth in a time of 13.30sec.
Tony Jarrett, who went out in the World Championship heats, gave a better indication of his ability this time around by taking third place in 13.21, with Mark Crear finishing 0.01 behind his American compatriot.
The race was preceded by a B version, in which Roger Kingdom, the 34- year-old American who set a world record of 12.92sec nine years ago, won in 13.36. He is one of a long line of athletes who have responded positively to the combination here of financial incentives and intense spectator appreciation. The meeting, with its annual budget of pounds 2.5m, has the financial clout to make it virtually obligatory for the world's leading athletes.
Merlene Ottey, a particular favourite, raised the noise level still further in the 100m as she held off the woman who beat her in Athens, Marion Jones, and her US colleague, Gail Devers, the Olympic champion, to win in 10.96 sec.Reuse content