Despite the move up to two weight classes for the UFC 196 main event, McGregor was still expected to get the better of the taller Californian who took the fight on just 11 days' notice following Rafael dos Anjos' injury-enforced withdrawal.

But Diaz, his face blood-stained from a tough opening round, caused a massive upset when getting full mount on McGregor and locking in a rear-naked choke to force the tap-out at 4:12 in the second frame.

The Dubliner's maiden UFC career defeat - and his first in any octagon since November 2010 - left the crowd in the MGM Grand Garden Arena stunned, especially as he had looked in control for much of the bout.

McGregor admitted afterwards: "Humble in victory and defeat. I'll learn, I'll grow. I'll face it like a man, like a champion."

#ConorMcGregor's thoughts after the fight...#UFC196 pic.twitter.com/kK1NAfQWyR

— BenchWarmers (@BeWarmers) March 6, 2016

"These things happen in MMA. I took a chance and it didn't work out.

"I took the chance going at 170 pounds. I thought I took the first round, I was inefficient with my energy. I respect Nate, he took the punch. He took the fight on short notice and done the job."

Stepping up 25 pounds for this welterweight contest, the 27-year-old Irishman moved well to connect with some strong left hands early on and negate Diaz's reach advantage.

McGregor's punching accuracy caused a cut on Diaz's right eye and while his right uppercuts and spinning kicks did not do much damage, most observers had him winning the first round 10-9.

Remaining on the front foot, the SBG fighter seemed to tighten his grip on proceedings with a solid start to the second stanza, landing a crisp left shot to the body and a couple more to Diaz's bloodied face.

Crucially, Diaz managed to break up McGregor's momentum with a stinging left to the jaw that set up an absorbing period of brawling. Both fighters unloaded punches and suddenly it was the Crumlin man who was fading and Diaz was the one connecting with powerful shots.

McGregor attempted a desperate takedown entering the final minute but the long-limbed Diaz maintained the pressure, countering quickly to lock in the decisive choke hold and earn the 12th submission victory of his 29-fight MMA career.

"I'm not surprised, motherf**kers," Diaz insisted, reacting to his triumph. "I knew it was going to be a slow start for me, because I'm always in shape. But if I'm not in the best shape, I've got to start slow and pick up as I go.

"I expected to dodge and slip a little more. I didn't have a lot of sparring for this camp. If I would have had a full camp, I don't think I would have been touched."

It was a night of upsets in Las Vegas as Holly Holm, the conqueror of Ronda Rousey last time out, was beaten by Miesha Tate who had a superb fifth round submission in their Women's bantamweight title duel.

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