The U.S. gymnast scored 58.999 points to finish 2.1 points ahead of China's Tang Xijing. Angelina Melnikova of Russia was third on 56.399.

Biles' margin of victory was her biggest at a world all-around event, and matched her winning margin at the 2016 Olympics, before she took a year off.

She finished her floor routine with a mic-drop gesture.

"It wasn't my best routine but we just thought it would be fun," she said. "I feel like right now actually I'm pretty confident in my gymnastics and myself and the performances I put out there, so I feel like I'm probably more confident going in today than I was at the Olympics."

No other woman has won more than three all-around titles. Biles' victory makes it seven wins in a row for the United States in the women's all-around, matching the Soviet Union's record streak at world championships in the 1970s and 1980s.

Tang wasn't even meant to be competing Thursday but became China's first all-around medalist in eight years. She'd qualified third-best of China's gymnasts, with only two per country allowed in the final. However, Tang was drafted in to replace teammate Liu Tingting, who fell on two routines in Tuesday's team final.

Tang said she didn't know she was contending for a medal until after finishing her final routine.

"I hoped to do what I'm like in training, and didn't really think too much about the results," she said through a translator. "I didn't even watch the results myself, so it was really surprising."

Biles' U.S. teammate Sunisa Lee placed second in qualifying, but her hopes of a medal were dashed when she came off the uneven bars. She finished eighth.

"I feel like I kind of let the nerves get to me a little bit, but it's all part of the learning experience," Lee said. "There's going to be a lot more meets to come before the Olympics, so hopefully I can kind of get myself back together for that."

France's Melanie de Jesus dos Santos had qualified third-best but fell twice on uneven bars and placed 20th.

Biles has won the all-around title at every world championships she's competed in, starting in 2013. She skipped the 2017 season, when Morgan Hurd won the gold.

In a sign of the U.S. team's depth, Hurd wasn't named to the team for this year's worlds despite also winning bronze last year.