Undisputed middleweight champion Bernard Hopkins takes on Robert Allen in Las Vegas on Saturday while Oscar de la Hoya challenges WBO champion Felix Sturm.
BBC Sport takes a look at what is at stake at the MGM Grand on a night being billed as "Collision Course".
Countdown to 18 September
Hopkins and De la Hoya must both win on Saturday to ensure their proposed September showdown goes ahead.
That match would be the most lucrative non-heavyweight bout in history, with De la Hoya alone expected to pocket $30m for his efforts.
Much like 1987's middleweight blockbuster between Marvin Hagler and Sugar Ray Leonard, it would be the division's unglamorous but unequivocal king against a dazzling legend of the lighter ranks.
Whatever the outcome, the fight would probably bring down the curtain on De la Hoya's career while it would likely be the 39-year-old Hopkins' penultimate bout.
Two fighters chasing history
Penultimate bout because the "Executioner" needs two more wins to reach 20 world title defences.
Says Hopkins: "History is at 20 for me - that is my goal and why I continue to stay focused and starving."
Meanwhile, the "Golden Boy" is bidding to become the first man to hold genuine world titles in six weight divisions.
"The reason I am still doing this is because of history," says the 31-year-old. "History for the sport, history for me - I know I can accomplish everything I have set for myself."
The obstacles
Hopkins has fought Allen twice already - a 1998 non-decision after Hopkins was shoved from the ring in the fourth round by referee Mills Lane, and a seventh-round stoppage for Hopkins in 1999.
An awkward southpaw, Allen (36-4, 27 KOs) has slowly but surely rebuilt his reputation and proved in their first encounter - in which he gave the champion a rough ride - he is no soft touch.
Meanwhile, Bosnian-German Sturm (20-0, 9 KOs) is a competent fighter with no notable scalps on his record but a once-in-a-lifetime chance to alter the course of history.
The 25-year-old won the WBO belt in September 2003 and has defended it once - the only two occasions he has been 12 rounds.
The likely outcome
Hopkins and De la Hoya are too close to achieving something truly monumental to leave anything to chance.
While Allen is a world-class fighter, Hopkins is an all-time great, still in awesome shape and has devoured a string of former world champions over the last two years.
As such, he will have too much for Allen and see to it that one half of the job is done.
As for De la Hoya, he is a very shrewd operator and would never have taken the fight if he did not think he could win it.
Sturm's record suggests he lacks a good whack and one would expect De la Hoya's immense experience and ring craft to carry the day and save promoter Bob Arum's blushes.
Job done, both fighters will then hurtle towards the collision itself - a hit that will shake the very foundations of boxing.