LAS VEGAS - Champion Khabib Nurmagomedov ended Irish fighter Conor McGregor's attempt to win back the UFC lightweight title when he sealed a brutal submission victory with a rear naked choke hold in the fourth round on Saturday.
The win prompted a mass brawl to break out in and around the cage, with a red-shirted fan landing several blows on McGregor before security intervened.
Both fighters were subsequently escorted from the arena by police and security.
No belt was presented and no speeches made, but the ring announcer declared Nurmagomedov the winner to a chorus of boos of the crowd.
McGregor, making a comeback to the octagon after nearly two years away, had looked dangerous in the early striking exchanges but as expected, Nurmagomedov quickly took the fight to the ground.
The Russian smothered him with his wrestling skills and prevented him from getting back to his feet for the rest of the round.
The Irishman was then wobbled by an early right cross from the Russian in the second round and the fight was soon on the floor again, but this time the Russian champion was able to keep the challenger from getting his back to the cage.
McGregor survived until the end of the round, giving a tired smile as the horn went, and in the third period he managed to keep the fight standing, tripping off shots to the head and body as he rediscovered his range.
However, it proved to be too little, too late, and the Nurmagomedov was once again on top in the fourth, sapping McGregor's energy with his excruciating pressure before the choke ended the fight 3:03 into the fourth round.
The victory stretched his professional record to 27-0 and handed the Irishman his second defeat in the UFC.
(Editing by Greg Stutchbury)