The Jamaican, who had looked in great shape in the morning heats, was never at the races after hitting the first hurdle and clattered several more to round off a disappointing defence of her title. Victory went to her veteran compatriot Dawn Harper-Nelson, the 33-year-old 2008 Olympic champion looking in remarkable shape as she won the race and then promptly performed a cartwheel in delight.
Favorite Kendra Harrison, who set the world record in the London Stadium previous year having missed out on Olympic selection, clattered too many barriers as she did in the semis and finished fourth in 12.74.
Competing at her first major global championship since 2013 and having overcome serious wrist, hamstring and achilles injuries, the Australian powered away from the field to win in 12.59 seconds. But when she clocked 12.48 seconds in the London Diamond League last month - her fastest time for five years - she realized she was in medal-contending form. Pearson and 400m hurdler Jana Pittman are the only two Australian track and field athletes to have won individual world golds.
Making the victory even more special was that Pearson had coached herself for the past year. "I watched her warm up out there out of the corner of my eye and they were doing things that I thought were a bit different to what she had normally done as part of her warm-up and I thought there were perhaps a few demons going through her head", Hilliard said.
"When I knew I felt that I knew it was in me to do it".
"I've worked so hard, I don't know what has just happened out there".
Former men's 110m hurdles world record holder Colin Jackson described the Australian's technique as "absolutely flawless" and that, combined with her famed winning mentality and now a body again able to match her mind, took her over the line.
Her next challenge will be winning a third successive Commonwealth title on home soil on the Gold Coast next year.
Nelson, Pearson's long-time rival, was excited to be back and win the silver again in London.
"I love this stadium. This is just so incredible to be a world champion again", Pearson, also the silver medallist in the Beijing Olympics, said.
"Silver tastes like gold tonight".
"It's hard to compare eras, I don't think you can, and it would be stupid of me to do that - Betty Cuthbert was a freak". "I am really excited to come out of this with a medal for the U.S".