Conor McGregor knocks out opponent to become new interim UFC featherweight champion

The Dubliner was in the most grave trouble of his career for almost the entirety of the fight but with just three seconds left in the second round, he turned the tide and floored Mendes with a punch that will undoubtedly send McGregor's phenomenal career into a new orbit.

The MGM's Grand Garden Arena had reverberated to and deafening Irish noise as McGregor made his way to the ring with Sinead O'Connor performing a stirring rendition of The Foggy Dew.

But it was Mendes who seemed the more stirred as the Californian raced into ascendancy.

McGregor had spun a kick towards his rival straight from the bell but he was soon sent spinning backwards as Mendes charged into the fight.

After much of the build-up had focused on whether McGregor would be able to prove those who doubted his wrestling skills wrong, he was very soon on the floor. Mendes pinned him down and connected with a wicked elbow that cut McGregor open above his right eye.

It was a jarring sight to see the undefeated Notorious one with blood spilling down his face. He had never bled in his UFC career to that point. Mendes had much the better of the rest of the round but McGregor, in trademark style, patted his opponent on his head at the bell and walked back to his stool.

When the break was over he walked straight back into the storm however as Mendes again floored him and looked for a submission. McGregor's defensive work, his heart and his refusal to open the door was remarkable.

When he hauled himself off the canvas with about 20 seconds left in the round it looked as he had weathered the storm and would regroup at the bell. The bell never came however as McGregor launched a devastating counter. A huge swinging left hand hit its mark and Mendes hit the floor for the first time in his career, never to get up.

Emotion poured from McGregor as he dropped to his knees in his moment of glory. 'I'm blown away by the support. I'm shaking here," he said as the decibel levels rocketed. "No one can take that left hand shot."

Mendes was gracious in the wake of the third loss of his career. "I want to thank Conor for even accepting on 2 weeks [notice]," he said. "The guy is tough. He's got the talk to back it up. These Irish guys are crazy. I wish we had had this kind of support here [in the US]. I'm never going to forget this."

The triumph earned McGregor the hardware he has craved for so long. On the most lucrative night in UFC history, it will also have earned him a massive pay day. But there will be an even bigger day coming next with McGregor now back on a collision course with original opponent Jose Aldo.

Win that, and the UFC have promised McGregor a first defence at Croke Park. After its most remarkable episode yet, the McGregor Show will roll on.

Elsewhere, there was dejection on the double for the two other Irish fighters on the record-breaking UFC 189 card. Cathal Pendred suffered the first loss of his UFC career as John Howard dominated all three rounds.

After raising the roof with as he entered the octagon to the strains of Put Em Under Pressure, Pendred never came close to doing just that. He looked cagey throughout with American Howard, who had lost his last three fights, enjoying much more success striking through.

Coach John Kavanagh pled with Pendred to get Howard to the ground but he never truly threatened. Somehow one of judges saw fit to score the fight in Pendred's favour but Howard triumphed on a split decision.

“It was difficult for me tonight," admitted Pendred, who had been in desperate need of a commanding performance. "John made it hard for me to do what we had planned on. I felt I would have the biggest advantage in the grappling but he was hard to hold down. He has great hips and he’s stronger than he looks. Hats off to him. It was his night and I’ll come back better."

Earlier Neil Seery took a tough loss in the second fight of the night. A clash of heads with Louis Smolka early in the first round didn't help matters for the veteran Dubliner, who lost a unanimous decision, 30-27 on all three cards.

“He was a lot quicker than I expected and he was excellent in the scrambles," said Seery. "His tank of gas was better than mine. Just an all-around tough bloke. I’m happy for him and I hope he goes very far in the UFC.”