There is more at stake here on Saturday night than the unification of three versions of the world welterweight title. The immediate future of boxing is in the experienced hands of Floyd Mayweather and Manny Pacquiao, as it pretty much has been since their parallel careers have threatened to cross, stretching back to 2009.

Other fine practitioners have flitted in and out of the universal consciousness since Mike Tyson generated heart-attack excitement over two decades, but these two champions, with 74 years on the planet and 20 world titles between them, stand apart – literally, from each other, until now.

And it is that teasing longueur that has stretched the patience of boxing’s audience in a fragmented era with only occasional highlights, many of them authored by these two fighters. If their gears do not mesh – which, given Mayweather’s penchant for boxing on the retreat and Pacquiao’s inclination to fight as if pursuing a burglar, is possible – the sense of anti-climax will be immense. If it is short, it will be dramatic; if it is long, it is more likely to resemble chess in shorts.

Day one of fight week in Las Vegas hums with opinion, both informed and uninvited, but the prevailing sentiment up and down The Strip is that nobody is bet-your-own-money sure about the outcome of their long-awaited collision at the MGM Grand Garden Arena.

Both are champions. Both are great fighters. Both are old. Those are ingredients that sow doubt, whatever the opposing camps would like you to believe.

With all the shaky conviction that seems to have gripped canvassed voters in the leadup to the general election in Britain, boxing fans are wavering like the wind in loud discussions in the sports bars and restaurants all over Vegas. Shop attendants ask, “Who do ya like Saturday?”, adding their own two cents’ worth. Barmen and waiters, hacks and real people, all have plenty to say, but few sound convinced.

Over the past week, I have met no one who is either unaware of the event or disinterested. Everybody is up for this, although there are pockets of caution.

In a city dedicated to gambling, the concept of a sure thing is as seductive as it is dangerous, and the Fight of the Century is no lock to be either a great contest or, according to one observer, the eye-watering financial bonanza its backers are predicting, although it will certainly generate record amounts of cash, perhaps as much as $400m.

Writing in Forbes magazine, Darren Heitner says the spread of 3.15m to 3.8m pay-per-view hits offered by bookmakers Sports Interaction is set too high, partly because the $100 being asked for HD TV access on Showtime and HBO will drive viewers towards, "alternative methods of receiving the content in this age of the Internet".

SportsbookReview.com’s editor in chief, Zack Jones, agrees. “I think three million is probably closer to where the line should be set,” he tells Heitner.

That, of course, still outstrips the previous high-water mark of 2.4m the night Mayweather beat Oscar De La Hoya in 2007 (which sold for $55, about half the current asking rate). The notorious "ballpark figure" mentioned casually in most discussions about the pay-per-view high bar is four million, conveniently round and therefore lacking scientific heft.

Heitner, for instance, thinks a lot of armchair sports fans will be exhausted at the end of Saturday – discussed here as, “the biggest day in sports history”, with the NFL draft, the Kentucky Derby and in baseball the Yankees playing the Boston Red Sox – and might have had enough by the time Mayweather and Pacquiao begin exchanging pleasantries.

Boxing relies for its health on regular exposure to large television audiences and the recent arrival of CBS, NBC and Spike TV, augmenting smaller outlets in truTV and BET, behind the big boys, HBO and Showtime, suggests either television executives have rediscovered their inner Tyson or are picking up signals that the sport has enough talent to inspire a revival.

The latter is a reasonable theory. The heavyweight division is always the barometer of how well boxing is playing with an audience wider than the hardcore, and Deontay Wilder’s emergence as a genuine world champion, armed with dynamic power and a strong personality, is what the fight game here has been waiting for since the disappearance of not-so-Iron Mike in 2005.

But, for now, the main man is Mayweather, with Pacquiao his perfect foil and striking opposite. Mayweather rules the industry, fighting who, when and where he wants for fabulous amounts of money. He is not universally liked, gives no hint of self-deprecation and has defensive boxing skills that ought to be a turn-off for bloodthirsty American fight fans.

Yet he holds audiences in thrall. Mayweather is a self-made phenomenon, negating all prejudice because of his gift for making money and his disregard for any opinion but his own. Scandal washes over him like a desert shower. His acolytes guard and cosset him from the poison of criticism, devout disciples of the strangest religion in sport, the Money Team.

Pacquiao, also, has fanatical supporters – most of the 90 million people who live in the Philippines, for a start. But he moves through life with monk-like serenity, untroubled by his own occasional problems, such as a $78m tax bill, or, until he became a born-again Christian and a responsible congressman, the attention of women who were not his wife.

These are the stars of the show this week. If they deliver, they will almost certainly have to do it again in September. However, Mayweather will be halfway through his 39th year by then and Pacquiao will be not far short of his 37th birthday.

They do not have much time to work their magic for their sport. But the odds are they will not disappoint us.