Juan Manuel Marquez's 'perfect punch' leaves questions over Manny Pacquiao future

Rematch – and fifth fight – on the cards but hopes for Mayweather contest ended by brutal KO

Bang, it's over.

The genuine rivalry between Manny Pacquiao and Juan Manuel Marquez has taken eight years, four fights, two hours of boxing and a punch that travelled less than six inches to reach some type of ending.

On Saturday night at the MGM in Las Vegas, a capacity crowd fell silent for the longest and most savage of seconds when Pacquiao fell unconscious to the canvas at the end of round six.

The great Filipino, a world champion at eight weights, was out cold for over a minute and the fourth fight between the two bruised and bloody men was over.

However, as they each received medical clearance for the beating they had taken in the brutal modern classic there was already bold and sensible talk of a fifth fight. "Why not?" said Bob Arum, the promoter of the fight.

On Saturday Pacquiao cleared in excess of $26m (£16.25m) and Marquez, who won for the first time in their series of fights, left town yesterday with as much as $10m (£6.25m) in his pocket. A fifth instalment would probably make Marquez $20m (£12.5m) and it is unlikely that Pacquiao, who is already the second highest-paid sportsman in the world, would make any less than he did on Saturday.

There are few wise heads in the boxing business in the aftermath of a super-fight in the casino city, but thankfully Pacquiao's long-term trainer Freddie Roach provided a degree of sanity as the dawn approached. "We need to look at the fight and I need to look at Manny," insisted Roach. "I want to be sure he is fine and I will be able to tell. I know him." Roach is correct and Pacquiao's clean bill of health after a CT brain scan at the hospital only tells part of the story.

A good trainer will know if his fighter is "gone", which is not a medical term, but it is one that correctly ends a fighter's career if the diagnosis is made. "If I like what I see he will fight, if I don't then he will retire," promised Roach, who admits to fighting too long as a professional boxer and not taking the advice of his trainer Eddie Futch when he was told to quit.

On Saturday night Marquez was trailing on all three cards by just one point when he connected sweetly with the shortest and most deadly of rights to send Pacquiao into oblivion. Roach claimed that the punch travelled two inches and he is probably right, but Pacquiao was charging forward, his right leg off the canvas, and Marquez was leaning into the lunge and at that perfect point of impact the fist found the chin and that was it.

"It was the perfect punch," said Marquez, who had vowed last year, when he dropped a controversial decision to Pacquiao, to never fight his nemesis again.

Pacquiao had been down heavily in round three, Marquez tumbled over hurt in round five and in round six, which Pacquiao was winning, and the fight had already been elevated to modern classic; the ending guarantees the fourth fight between the pair a special place in boxing history.

The bout between Pacquiao and Floyd Mayweather Jr, which was first seriously discussed in 2007 and has been at the centre of all boxing fans' desires since then, appears now to have vanished forever. I hope that it has gone for good because the greed during the last five years has been sickening.

It is too simple to blame one camp for the failure of the fight to take place, but hopefully the lost opportunity will serve as a harsh warning to all future fighters that fail to meet their natural rivals at a time when it still matters. Pacquiao against Mayweather in 2008, 2009, 2010 and 2011 would have been the most lucrative fight in history; it will instead always be the greatest fight to have never happened and that is not a bauble worth owning.

There does, sadly, remain a few rumours surrounding the enhanced shape of Marquez since he started working with specialist conditioner Angel Hernandez, a shadowy figure from the dark fringes of sporting alchemy.

The fighters were both tested before and after the fight by the local athletic commission, but there is most certainly a need for random testing, which is one of the main reasons that Mayweather Jr refused to agree terms to fight Pacquiao.

The proliferation, unregulated it has to be said, of specialist conditioners inside the closed camps of elite boxers is a concern in the boxing business; there have been several high-profile failed drug tests of world champions in America this year and the attitude to their disgrace has been far too lenient.

On Saturday night the sport of boxing delivered a sensational night with just about the only ending that nobody predicted.