Conor McGregor stunned Jose Aldo with a knockout after 13 seconds to become the undisputed featherweight champion at UFC 194 in Las Vegas.
The astonishing finish came as Aldo charged forwards aiming a right punch that McGregor evaded, and the Irishman whipped a straight left hand that clattered against the Brazilian's jaw.
Aldo fell face-first and referee John McCarthy immediately dived in to save him from further punishment.
It represented the completion of a remarkable rise to fame for McGregor who only debuted in the UFC two years ago - Aldo, meanwhile, had been the champion for six years and hadn't lost in a decade.
McGregor said: "Nobody can take that left hand shot. He's powerful and fast but precision beats power and timing beats speed.
"Jose was a phenomenal champion who deserved to go a little bit longer."
Elsewhere, Luke Rockhold is the new middleweight champion after inflicting Chris Weidman's first career defeat.
The California fighter earned a fourth-round stoppage over his New York rival with strikes on the ground. Rockhold had previously looked set to force a stoppage as the clock ticked towards the end of round three but, as he mounted Weidman and hit him repeatedly, the referee let them continue.
Rockhold had caused significant damage with his left-sided kicks and as Weidman tired he found increasing success with his takedowns, before eventually forcing the conclusion after 23 minutes.
Yoel Romero took a split decision win against Ronaldo 'Jacare' Souza, Demian Maia put on a jiu-jitsu masterclass to out-point Gunnar Nelson and Max Holloway earned a unanimous decision win over Jeremy Stephens.