Jason Jackson ended Yaroslav Amosov’s 27-fight win streak to win the welterweight title at Bellator 301 in Chicago, Illinois.
Jamaica’s Jackson, 33, stopped Ukraine’s Amosov, 30, with a flurry of punches in the third round at the Wintrust Arena.
The defeat was the first of Amosov’s career with Jackson winning his maiden Bellator world title.
“This feels like a dream and I woke up and I’m still dreaming,” said Jackson.
“Every man has a dream and every man has a nightmare and you’re looking at him.”
In the co-main event, Patchy Mix submitted fellow American Sergio Pettis in the second round to unify the bantamweight division.
Mix, 30, put on a beautiful display of grappling to secure a rear-naked choke and secure his first Bellator undisputed title.
The bouts were fought out while the future of Bellator remains unclear, with no future shows announced.
Bellator has been up for sale for a number of months, with fellow promotion the Professional Fighters League (PFL) touted as potential buyers, but a deal has yet to be finalised.
Jackson upsets the odds to beat Amosov
Amosov’s last bout was a convincing win over Logan Storley in February to unify the division. That was his first contest since stepping away from the sport for a period to help the Ukrainian army’s attempt to defend the country against Russia’s invasion.
The 30-year-old had won all 27 fights since debuting in 2012, with eight of those coming in Bellator, to evolve into one of the promotion’s biggest stars.
Jamaica’s Jackson, meanwhile, had won six successive fights heading into the bout with Amosov, with the 33-year-old beating two former world champions – Douglas Lima and Benson Henderson – in his past four contests.
During fight week, Jackson said people were “sleeping on him” and he backed up his words with a fine performance to upset pre-fight favourite Amosov.
Amosov, who had out-wrestled the majority of his opponents during his undefeated run, was not able to take Jackson down in the way he had done with previous opponents.
In the first two rounds, repeated takedown attempts were snuffed out by Jackson, who responded with the cleaner punches of the pair.
As a frustrated Amosov continued to try to take the fight to the ground without success, Jackson started to open up with his striking in the third round.
He landed a strong knee and uppercut on Amosov, before later dropping the Ukrainian with a straight left-right combination.
Jackson then followed up with a flurry of punches before the referee stepped in to end the fight.
The victory secures Jackson his first Bellator world title in his ninth bout with the promotion.
Mix lives up to ‘Human Backpack’ nickname
The interim title was created when defending champion Pettis, 30, suffered a torn anterior cruciate ligament (ACL) in 2022 and had to pull out of the Bantamweight Grand Prix.
Mix then won the tournament and the interim belt, setting up the undisputed title fight with Pettis, who returned to action in June, beating Patricio ‘Pitbull’ Freire.
The pair also have history, sharing numerous moments of respect during fight week, with Mix being a trainer partner for Pettis’ UFC fight with Brandon Moreno in 2017.
With 12 submission wins going into the fight, Mix adopted the nickname ‘The Human Backpack’ because of his expert back-taking skills, and he lived up to it once again.
Mix controlled Pettis on the ground for the majority of the first round, before successfully utilising his grappling again in the second.
Pettis showcased his flamboyant striking, throwing an axe kick and a spinning back elbow, before Mix neutralised his attacks with another takedown.
After gaining back control of Pettis, Mix then locked in a rear-naked choke for the victory.
“I’ve been grappling so much this camp. I knew three years ago against Juan Archuleta I should have trapped his arm [in defeat]. I had to come back for this belt,” said Mix.
“I’m the best in the world at 135lb. It doesn’t matter if you put King Kong [against me], I’d [beat him].”
In the Lightweight Grand Prix, Russia’s Alexandr Shabliy beat Brazil’s Patricky ‘Pitbull’ Freire – Patricio’s brother – to reach the final of the tournament, which has a winner’s prize of $1m (£802,000).
Shabliy, 30, put on a display of slick counter-striking to earn a unanimous decision win over the 37-year-old former champion.
Elsewhere, former featherweight champion AJ McKee earned his third successive win since moving up to lightweight, outpointing fellow American Sidney Outlaw, and Raufeon Stots beat bitter rival Danny Sabatello.