Gene Tunney defeating Jack Dempsey, Max Schmeling beating Joe Louis, Cassius Clay befuddling Sonny Liston, James ‘Buster’ Douglas knocking out Mike Tyson – heavyweight boxing has a rich history of astounding upsets.

That’s what happens when men who weigh 200lbs-plus start throwing leather. When the big boys go, the concept of a ‘good chin’ gets thrown out the window and one punch can change everything.

Australia’s Alex Leapai, who tackles long-term incumbent Wladimir Klitschko on Sunday morning (AEDT) in Oberhausen, Germany, will become a member of that upset club should he prevail. 

In fact, were Leapai to win he would surpass those results and enter Balboa territory.  

Rocky touches them up with Ivan Drago. Photo AAP

Sylvester Stallone’s Rocky depicted a Philadelphia club fighter who is handed a shot at the world heavyweight title and shakes the hell out of champion Apollo Creed against all the odds.

Klitschko hasn’t been defeated in 10 years, and has considerable advantages in height and reach. It will be a sure-fire case of David and Goliath – but Leapai’s slingshot will be armed with guided missiles instead of pebbles.

Leapai can punch like a mule kicks, but the challenge for him will be manoeuvring his shorter frame under Klitschko’s ramrod jab to get within range. Many have tried and failed.

The 34-year-old, who lives in Queensland with wife Theresa and children Cyanne, Maria, Menimi, Alex Jr, EJ, and Ivona, will need to have the night of his life in Oberhausen.

Klitschko’s height advantage is considerable. Photo: AAP

Leapai is a poster boy for boxing’s ability to regenerate.

In 2005 he was sentenced to four years in jail for assaulting four bouncers outside a nightclub.

He emerged a different man, having found religion as he embarked on a career beating people up, and from all accounts has been a model citizen as his boxing career has progressed.

Now he has the chance to make history, as the first Australian man to challenge for a world heavyweight title in a century.

No matter how much the bookies tend to feel a man will win, accidents can happen – it’s part of heavyweight boxing’s appeal.

But that appeal has waned considerably in recent years – with the Klitschko brothers, Wladimir and Vitali, easily dominating the division against a succession of opponents with neither the size or skill to trouble them.

Briton David Haye had the attitude, but while his talk was first rate, his walk was sadly lacking.

Bluntly, heavyweight boxing is in a dire place – and has been since the retirement of Lennox Lewis a decade ago.

“Yo Theresa, I did it…” Photo: Getty

The 1990s, when Lewis, Riddick Bowe, Evander Holyfield and Mike Tyson plied their trade, seem like a distant dream.

Even the 1980s, at the time regarded as something of a nadir as Larry Holmes ruled and a procession of uninspiring contemporaries like James ‘Bonecrusher’ Smith, Tony Tubbs, and Trevor Berbick plodded, seem positively electrifying by comparison.

Tyson’s arrival in the mid-80s was a like bolt of lightning, bringing a whole new audience to the sport, record purses and an interest not seen since Muhammad Ali was in his pomp.

The sport is crying out for another Tyson-shaped broom to sweep it clean and get people excited again.

Alex Leapai will not be that broom – at 34, he has already been beaten four times, by men with none of the class or seasoning of Wladimir Klitschko.

But his power makes him a live underdog. Klitschko has frailties – he’s been knocked out three times, so his chin is suspect.

Whether Leapai can catch lightning in a bottle and land something big on Sunday will be intriguing.