As the 31-year-old Texan reacted to the information on the clock he raised his arms and produced a dazzling smile the like of which we have not seen from him since he shattered the world 200m record at the Atlanta Olympics. Johnson finished ten metres clear of the field after accelerating to full speed over the final 100m.
Britain's two contenders, Mark Richardson and Jamie Baulch, were run out of the medals in a separate race going on in Johnson's wake. Richardson was sixth in 44.65sec - another massive disappointment for the man who missed out on the European and Commonwealth titles last season - while Baulch was last in 45.18sec.
The rumours of injury surrounding the defending 400m champion, Johnson, when he arrived here have disappeared into a sky as clear as the one above the stadium, to the point where the American - who ran 43.95sec in his semi-final despite appearing to ease down 100m from the end - had rightly predicted a world record in today's final.
"I'm going to give it my best shot," said Johnson, whose previous best of 43.39sec - set in winning this title four years ago - was only 0.10sec outside the mark established by fellow American Butch Reynolds in Zurich in 1988. "I've never run that fast shutting down so far out," he said. "I shut down with more than 90 metres left."
The statistics sheets bear witness to the extraordinary sway he has held in the one-lap event. Before his surprise defeat by both Mark Richardson and Iwan Thomas at last year's Oslo Grand Prix, when he was returning after a hamstring injury, his unbeaten record in major races stretched back to 1989, and he ran under 45 seconds on 58 occasions. Before last night's race, he had compiled seven of the 10 all-time best marks and 13 of the top 20.
Katharine Merry, running in her first championship 400 metres event, finished fifth in the final in a time of 50.52sec as Australia's Cathy Freeman retained her title in a winning time of 49.67sec, the fastest of the season.
Merry, drawn in the inside lane, worked hard to hang onto the pace as the field came around the final bend, but found herself increasingly detached from the leading quartet, of whom Ania Bucker of Germany earned silver in 49.74, and Lorraine Graham of Jamaica took bronze in 49.92.
Merry's time was outside her best of 50.21, established in reaching yesterday's final.
Marion Jones, whose dominance in the 100 and 200 metres has matched that of Johnson over the last three years, confirmed yesterday that she will take no further part in the championships at which she hoped to win four gold medals.
Having been wheeled off the track on a stretcher after collapsing with back spasms 50 metres from the end of Wednesday's 200m semi-final, she has been treated by two US doctors who have accompanied her here, but her coach, Trevor Graham, said yesterday that she would not return to the track to seek a medal in either the 4x100 or 4x400 metres.
"I'm not going to put her out there, no way," said Graham. "We discussed it with her and she's okay with it. She's disappointed, but she's in good spirits. There is a little pain and soreness, but she can walk. She's not dead."
The 23-year-old from Thousand Oaks, California, won the 100m title on Sunday night in a championship record of 10.70sec but had to settle for bronze in the long jump, where her body was repeatedly jarred because of her awkward style. Thus what was supposed to be a dress rehearsal for next year's Sydney Olympics, where she intends to go for an unprecedented five gold medals, has had the curtain precipitately brought down upon it.
She now faces a race to regain fitness in time to contest the Brussels meeting next Friday, where she must win if she is to retain a chance of sharing the $1m jackpot on offer to those athletes remaining unbeaten throughout all seven Golden League events.
For Jonathan Edwards, still trying to come to terms with his disappointment at only getting the triple jump bronze medal, Brussels is not on the agenda.
The 33-year-old Gateshead athlete plans to end his season the following day at the USA versus Britain match in Glasgow - but he confirmed yesterday that he would go on to contest the Olympics next year.
Given his state of mind following his shattering defeat on Wednesday night, however, he was not able to raise much enthusiasm for that prospect yesterday.
"The thought of picking myself up and starting training for Sydney is not a particularly pleasant one right now," he said. "But I will do." He was unable to explain why he had performed so badly in a final, in which he had hoped to jump beyond 18 metres, as he had done in winning this title four years ago.
"I haven't seen the video yet, but I expect it will be a horror story," he said. "I was getting a lot of over-rotation on the board, which manifested itself in the step phase, so I was never in position to get in a good jump."
Britain thought of protesting against the jumps of the winner, Friedrich of Germany, on the grounds that he had taken off outside the lines of the runway.