Injured Carlos Ulberg knocks Jiri Prochazka out cold to win UFC gold as Donald Trump watches on

Carlos Ulberg stunned the world at UFC 327 as he battled through a serious knee injury to knock out Jiri Prochazka and claim the vacant light-heavyweight title.

With US president Donald Trump watching cageside at Miami’s Kaseya Center, Kiwi fighter Ulberg entered the fight as the underdog with Prochazka, a former champion whose first reign was curtailed early by injury, seemingly well placed to reclaim the crown at 205lbs.

Hoping to pull off an upset against the crowd favourite in Miami, things started disastrously for Ulberg, who tumbled to the mat after tangle of legs that resulted from the ever-intense Prochazka pushing forward.

Ulberg quickly got back to his feet but was evidently hurt, blowing out his right knee in the unfortunate altercation, something Prochazka spotted and immediately started to target. Two sharp leg kicks to the healthy leg followed, with Ulberg then buckling as he tried to respond with punches.

Carlos Ulberg (right) injured his knee early into his main event with Jiri Prochazka (Getty Images)

US president Donald Trump was watching from cageside (Getty Images)

Despite now holding the clear advantage inside the very first round, fan-favourite Prochazka, famed for his all-action fight style, gestured to Ulberg that he wanted to stand and bang, giving “Black Jag” a way back into the fight. This would lead to the Czech’s demise.

Ulberg remained heavily hampered by his right knee, with commentator and former two-division UFC champion Daniel Cormier speculating that he “might have torn something”. Ulberg fell to the mat once again as he threw a high kick with his strong left leg, unable to put any significant weight on the right.

But as Ulberg stumbled back into the pocket, looking there for the taking, he threw a bomb of a left hook that knocked Prochazka down, pouncing on him with vicious ground-and-pound to put him out cold before the referee intervened, with Ulberg pulling off one of the most shocking, spectacular title wins of all time.

(AP)

"I blew out my knee, but I never ever counted myself out," Ulberg said in his post-fight interview. "I knew all I needed was that one shot and I ended up getting it. So I knew that Jiri was hesitant to come forward. And as soon as I landed my left hand he's going.

“I’m going to sort this knee out but we’re the champion.

"It's about getting those moments and we found that one kill shot. He said he could hurt me but you can’t hunt what you can’t kill.”

(IMAGN IMAGES via Reuters Connect)

For Prochazka, it meant more title heartbreak, having previously failed to regain the light-heavyweight against Alex Pereira in one of two losses to the former champion, who relinquished the belt at the end of February to move up to heavyweight.

He admitted the error of his ways after the fight, regretful of the “mercy” he gave to a clearly injured Ulberg.

"I felt so sorry with him, and this is one of the biggest lessons in my life," said a dejected Prochazka, holding back tears. “I still can’t understand… that fight was won, I had it, it was in my hands. I saw his injury, and... f***.

“I will be back. Life is about that, learn and be better."