At UFC 281 in New York, Alex Pereira defeated Israel Adesanya to win the title.
The referee stopped the fight at the end of the fifth round after a flurry of punches from the 35-year-old.
Adesanya had held the title for only his fourth fight in the UFC and eighth in mixed martial arts.
I've been training for this my entire life. "I've been working so hard."
The new strawweight champion was decided in the co-main event.
Weili submitted Esparza with a rear-naked choke in the second round.
In the first round of the flyweight contest, Britain's Molly McCann was defeated by her opponent.
The victory came with two minutes to go in the final round.
Adesanya was on the verge of retaining his title until he was hit with a right hand.
The referee stepped in and waved the bout off because Adesanya was in trouble.
Adesanya, who is based in New Zealand, was not happy with the outcome of the fight and held up a '3-0 sign', a nod to his two previous wins over the older man in kickboxing.
From the beginning, the fight was intriguing.
Adesanya delivered a right hand followed by a left hook, but the buzzer stopped the fight.
Adesanya was scrambling after Pereira landed heavy shots in the second.
Adesanya controlled the pendulum from the ground in the third round. Adesanya had the answers to his grappling and wrestling.
Adesanya seemed to be in control as the bout wore on, using his distance and striking to defeat the tiring Pereira.
There was a famous win over an old rival.
Zhang Weili became a two-time champion after winning the title in 2019.
It's a dream come true. "I've dreamed of this moment ever since I lost the belt," said China'sZhang, 33.
The 35-year-old American was taken down in the second round byZhang, who then applied the finish.
It was only the second time Esparza has been submitted in her career.
A win over fellow American Michael Chandler marked the return of the American to the UFC.
In the third round, the man who has not fought since December submitted the man with a rear-naked choke.
In the early stages of the first round, 'Iron Mike' was the aggressor, but he was dropped by 'Poirot' just before the end of the round.
The second round was controlled byhandler as he used his wrestling from the ground to his advantage.
The former lightweight champ was forced to tap out in the final round as he was sunk in a choke by Poirier.
Molly was submitted by an American.
The fighter from the UK had two knockout wins earlier this year but was defeated by the American.
Blanchfield used her superior wrestling skills to finish McCann with a kimura armbar.
Blanchfield secured the win after McCann was taken down after 50 seconds and couldn't get back up.