LAS VEGAS — A vicious, intentional knee to the head of a downed Aljamain Sterling cost Petr Yan his bantamweight title on Saturday at Apex on the main card of UFC 259.

Sterling was on his knees and as he raised his head, Yan belted him in the face with a right knee that snapped Sterling’s head back as if he were on a head-on crash at 65 mph.

Referee Mark Smith stopped the bout, and after several minutes, when it was clear that Sterling was physically unable to continue, Smith disqualified Yan. The end came at 4:29 of the fourth. At the time of the stoppage, Yan was up 29-28 on two judges' scorecards while Sterling was winning 29-28 on the third judges' scorecard.

It was an ignominious end to a stellar bout that was contested at a high pace and with great skill on both sides. It showcased everything that is great about MMA, with the men going after each other on the feet and on the ground.

Yan dropped Sterling in the first, but it was a back-and-forth round in which each man gave as good as he got.

Yan seemed to be gaining momentum in the third and the fourth and his shots were appearing to have an impact on Sterling. But the fight ended in inexplicable fashion when Yan appeared to lose his composure.

When Sterling was down, Yan stood over him briefly, as if waiting for him to rise. Several times in the bout, Sterling was on his back with Yan standing over him, kicking at his legs, before allowing him up. This time, Sterling was on his knees, but Yan hovered over him.

Then, as Sterling raised his head, Yan stepped forward and ripped him with a right knee to the face. The force of the blow was heard 40 or 50 feet away, and Sterling fell over onto his back.

Twice, the ringside physician came into the cage to check on Sterling. After the five-minute wait, Smith called off the bout and disqualified Yan.

It made Sterling the champion in a most unusual way, but he wasn’t about to say no.

More from Yahoo Sports:

• Thamel: Les Miles' time at Kansas must end

• WWE documentary tells story of Heaven Fitch

• Mark Pavelich, Miracle on Ice star, dead at 63