McLaughlin blazed home in 50.68 seconds to set the first world record at this year's championships, finishing well clear of silver medallist Femke Bol of the Netherlands.
Sydney McLaughlin broke her own 400m hurdles world record to win the gold medal in 51.46 seconds at the Tokyo Olympics.
Just a few hundred officials and dignitaries were in the stands of the 68,000-seat venue to watch the spectacle which included Japan Emperor Naruhito declaring the Games open.
The 2016 Olympic champion's blistering display sliced more than one-tenth of a second off the previous record of 52.34 sec, set by Russia's Yuliya Pechonkina.
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