UFC fighter delivers most brutal flying knee

Diego Rivas has delivered one of the most horrific blows in UFC history after felling his rival with a brutal flying knee at Fight Night in Las Vegas.

Dominated by Noad Lahat through the first round, Rivas, who trailed 22-7 in strike count to his experienced rival, knew he needed to execute a knockout blow if he was to have any chance of stealing victory.

And early in the second round, the Chilean fighter delivered with a strike that will long be remembered by fight fans.

Standing in the middle of the ring, Rivas pounced as his opponent went low for a takedown move, crushing Lahat's face with a flying knee that connected with a sickening crunch.

After a number of hammer punches, the ref quickly called an end to the fight as Lahat lay out cold on the canvas.

The sudden and violent end to the fight quickly lit up social media.