Anthony Joshua's career on knife edge after defeat to Andy Ruiz

The final blow, when it came, was as crushing as it was inevitable. A dazed and confused Anthony Joshua, one of the best athletes in the world, looked bemused and belittled as referee Mike Griffin decided he was no longer fit to continue.

His eyes briefly widened in surprise but the predominant emotion evident on his face was one of relief that it was all over.

And that's why Anthony Joshua's career hangs in the balance; because his defeat to Andy Ruiz was no fluke. This was no lucky punch out of the blue. This was a systematic dismantling of the man who has dominated the heavyweight division for the last five years.

Joshua has gone from kingmaker in the division - the one fighter who had the ability to shape his own destiny - to someone who has become a bit of a laughing stock.

His two biggest rivals reacted in very different ways - Deontay Wilder chose to put the boot in while Tyson Fury was more classy.

But neither of them will be quaking in their boots at the prospect of facing Joshua now - and while he has no belts they no longer need him.

Joshua's future hangs entirely on the rematch between him and Ruiz - win that in emphatic fashion and reclaim his belts and nobody will remember the defeat.

Lose and his career will be effectively over.

So, why did he lose? Well, the truth is it had been coming. Since his epic victory against Wladimir Klitschko when he could so easily have lost, Joshua has appeared vulnerable.

In his three fights since, against Carlos Takam, Joseph Parker and Alexander Povetkin, he has looked slow, heavy-legged and one dimensional. He is a supreme athlete but many of the critics will now be questioning his skills as a supreme boxer.

The other question that many have asked is whether Joshua took his eye off the ball. With the prospect of a title unification bout against Wilder or an all-British classic against Fury on the horizon, he may have forgotten about the fighter that was right in front of him.

He learned a key lesson here. An underestimated boxer is a dangerous boxer and Joshua found that out.

Joshua must remain positive if he is to climb to the top of the mountain again. He's not the first boxer to lose when he considered a heavy favorite and he won't be the last. How he reacts now will define his legacy.

The early signs are promising. He made no excuses after the fight and hasn't made any rash decisions in the aftermath.

Outside of the ring, he has shown the class of a true champion. He must now show it in the ring if he is to regain his place at the top of the sport.