The bespectacled 16-year-old, who was born in China and adopted as a toddler, followed in the footsteps of celebrated compatriot Simone Biles — ably shouldering US hopes after national champion Ragan Smith withdrew minutes before the competition with an ankle injury.
It was a stunning World Championships debut for Hurd, who was sixth at the P&G Championships in August but secured a place on the four-woman US team for the championships at a selection camp in September.
“It’s crazy that I was even competing here,” Hurd said. “To think that I won is just the most surreal feeling in the world.”
Hurd won with a total of 55.232 points, denying home hope Ellie Black of Canada who took silver with 55.132.
Russian Elena Eremina was third with 54.799, with Mai Murukami narrowly missing the podium with a total of 54.699.
Hurd sealed the win with her final routine, the floor exercise, erasing a deficit of two-tenths of a point to surpass Black.
It was a disappointment to fans at the 1976 Olympic venue, but Black became the first Canadian gymnast, man or woman, to win an Olympic or world all-around medal.
Hurd continued a long streak of success for US women in all-around competition.
An American woman has won every Olympic or world all-around title since 2011.
Hurd opened the competition by scoring 14.533 on the vault, which put her in fourth.
She was tied with Black for the lead after the second rotation, earning 14.300 on the parallel bars.
A 12.666 on balance beam left her in second going into the final rotation, and her floor exercise score of 13.733 — despite stepping out of bounds on her third tumbling run — was enough.
The competition lacked the top four finishers form last year’s Rio Games.
Two competitors touted as favorites going into the week were also absent — Smith and Romania’s Laris Iordache.
Smith left on crutches after hurting herself warming up for her opening vault.
USA Gymnastics said she was taken to hospital for X-rays.
Iordache, a two-time world all-around medalist, tore an Achilles tendon warming up for floor exercise before qualifying on Wednesday — three days after Japanese superstar Kohei Uchimura pulled out of the men’s qualifying with torn ligament in his ankle.
In Uchimura’s absence, China’s Xiao Ruoteng won the men’s all-around title on Thursday.
Men and women will be back on Saturday and Sunday for individual apparatus finals.