The 22-year-old American prodigy left rivals trailing in her wake at Hayward Field as she took gold in a stunning time of 50.68sec -- the first time any woman has ducked under the 51-second barrier.
McLaughlin's incredible performance sliced more than half a second of her own world record of 51.41sec, set at the same venue during the US trials last month.
Femke Bol of the Netherlands took silver in 52.27sec while McLaughlin's team-mate and defending champion Dalilah Muhammad of the United States took bronze in 53.13sec. "Honestly I just wanted to go for it," McLaughlin said afterwards. "The last 100 really hurt, but I'm grateful to have this crowd.
Go Team USA!" Bol and Muhammad would have had realistic hopes of challenging McLaughlin for gold before the race. But McLaughlin was in a league of her own almost from the gun, surging clear of Muhammad with a blistering opening 200m and coming off the final bend several meters clear of her rivals.