(CNN)George Kambosos Jr. produced one of the shocks of the years as he beat Teofimo Lopez to become the unified world lightweight champion on Saturday night.
The unfancied Australian, who came into the fight a heavy underdog, knocked Lopez down in the first round and survived being knocked down in the 10th round before winning on a split decision from the judges.
Kambosos won 115-111, 113-114, 115-112 on the judges' cards to claim the WBA, WBO, and IBF belts in a Madison Square Garden's that was almost entirely behind home-favorite Lopez.
"I believed in myself, I backed myself," the still unbeaten Kambosos said afterwards.
"I said it time after time: 'You might not believe it, but I believe in myself.' And look at me now. I've got all the jewels. I'm not the king, I'm the emperor because I come to every other country and I take them out one by one."
Lopez had initially won the belts 13 months ago in Las Vegas after beating Vasiliy Lomachenko.
His highly-anticipated defense was much delayed for numerous reasons, including having to pull out of a fight in June after contracting Covid-19.
But he eventually took to the ring against Kambosos, with the promise of producing a first-round knockout.
However, the American was the one who ended up on the canvas after an explosive first round, in which both fighters showed their power.
The pair exchanged big blows throughout the rest of the fight -- with Kambosos having to survive being knocked down himself later on.
But by the end of the bout, it was the champion Lopez who looked the worse for it, with his left eye and his nose bleeding profusely.
It was the first loss of Lopez's burgeoning boxing career, and a result that he was not pleased with afterwards.
"I don't care what anybody says," the 24-year-old said. "I won tonight. At the end of the day, I've been here, I've done it. Look, I'm not a sore loser. I take my wins like I take my losses.
"At the end of the day, I'm a true champion. I came out here, I did what I had to do, and I went out there and I did my best. ... This is the takeover. We don't stop; we keep coming."
In what is a stacked lightweight division, Kambosos has already been called out by Devin Haney, who holds the WBC lightweight belt.
"Congrats (Kambosos) well deserved victory you worked hard for it! Let's make it happen for all the belts! #RealUndisputed," Haney tweeted.