Manny Pacquiao wants Floyd Mayweather Jr and now, at long last, it now appears Mayweather wants Pacquiao. But for anyone who has held even the mildest interest in seeing the two welterweight kings collide, the reality of the fight taking place in 2015 is still a long way away.

Mayweather breaking his silence on the potential showdown was significant and his follow up interview with Fight Hype this week where he promised he and his entourage would handle negotiations like "true professionals" also bore promise.

But good intentions will only get this so far; the complications that have undermined the most eagerly anticipated match in recent memory are fully capable of arising once again unless those same old mistakes are avoided and lessons are learned. IBTimes UK takes a look at what has gone wrong.

Failed talks round one

In 2009, there was no greater time for a showdown between the welterweight's elite who were coming into the peak of their powers. Coming off the back of victories against Juan Manuel Marquez and Ricky Hatton respectively, Mayweather and Pacquiao sat down to talk terms with an initial 50-50 split of the fight's purse proposed.

That offer was undermined by Mayweather's demand that Pacquiao undergo Olympic-style drug tests to be carried out by the United States Anti-Doping Agency – a request not enforced by all professional boxing's governing bodies – in a development that soured those promising early exchanges.

Golden Boy promptly announced the fight was off due to the Filipino fighter's refusal to comply with those tests. Top Rank CEO and Pacquiao's promoter Bob Arum later stressed Pacquiao was willing to provide blood samples before the press conference and immediately after the fight but not before the weigh-in, fearing they would interfere with his final preparations.

Pacquiao's camp appeared open to the possibility of scheduled tests or those conducted within a cut-off date of seven days before the fight. But with no progress by early 2010, the fight was officially by the wayside, despite the impartial mediation of retired federal judge Daniel Weinstein.

What's changed since then? Pacquiao has repeatedly claimed since the original fight was scrapped that he is willing is undergo the controversial blood tests. He willingly got on board with tests conducted by the Voluntary Anti-Doping Association (VADA) for his 2013 bout with Brandon Rios and in his most recent fight against Chris Algieri. If Mayweather's demands were met with scepticism five years ago, they are downright laughable now.

Failed talks round two

For better or for worse – usually the latter – Bob Arum has played an integral role in talks over the last five years.

In June 2010, he again dangled the possibility of the fight in front of a baying audience when he announced the dispute over blood testing was over and an agreement had been met, throwing the gauntlet down to Mayweather to sign the deal for a proposed November fight within the next two weeks.

Top Rank handed weight to his claims, cheekily reinforcing his comments by placing a "Mayweather's Decision" countdown clock on their website.

The deadline passed, prompting talk that Mayweather had ducked the challenge. But the challenge never existed, not in any formal manifestation, anyway.

Arum claimed he had laid out basic terms with HBO Sports president Ross Greenburg who had in turn, spoken to Al Haymon, another representative of Mayweather.

What Arum had passed off as an agreement amounted to little more than old demands being put on the table again, something that was swiftly and decisively pointed out by Mayweather Productions CEO Leonard Ellerbe who added: "Either Ross Greenburg or Bob Arum is not telling the truth, but history tells us who is lying."

What's changed since then? Quite what Arum was attempting to accomplish with this ploy four years ago is still a bit of a mystery. Any more ill-fated publicity stunts could be fatal to the chances of this fight ever happening.

Failed talks round three

In an usual twist, the American justice system provided hope of Mayweather v Pacquiao in 2012 when they pushed the American's 90-day jail sentence for battery back until June, clearing the way for a meeting in on 5 May. Four days after his legal reprieve, Mayweather called out his adversary on Twitter.

Following the announcement, Arum, who had been all over the May showdown months earlier, responded by telling the Philippines Times that June 2012 was now preferred date with the initially proposed 5 May "impossible", citing a cut Pacquiao had suffered during his win over Juan Manuel Marquez the previous November as the reason for the delay.

A breakthrough appeared to beckon when Mayweather and Pacquiao got on the phone with each other to thrash out a deal, only for exorbitant numbers to once again derail proceedings. Pacquiao was offered a flat fee of $40m (£26m) to take the fight but nothing from the American pay-per-view takings that were estimated to be worth around $150m (£96m).

To the surprise of absolutely no one, the offer was rejected.

What has changed since then? Reported shares of the fight's purse have ranged from 40-60, 45-55 (both in Mayweather's favour, of course) and 50-50 over the years. Now it appears Pacquiao is not too fussed about what he earns. "Mayweather can get the amount he wants," he recently said. "As early as January this year, I challenged him to a charity fight. Until now, he has not agreed to it. So, money is not the issue in our fight."

Failed talks round four

Mayweather and Arum's acrimonious split in 2006 has cast a shadow over talks for the Pacquiao fight ever since.

The unbeaten American paid $750,000 (£480,000) to get out of his contract with Arum and Top Rank, claiming he failed to be fully paid for fights dating back to 2005 with Arturo Gatti and in 2006 with Zab Judah before he became the transcendent giant of the sport he is today.

The spat has since simmered and in 2013, Mayweather revealed the extent of the animosity between the two, vowing a fight between him and Pacquiao would never happen due to Arum's role in any negotiations.

"We all know the Pacquiao fight, at this particular time, will never happen, and the reason why the fight won't happen is because I will never do business with Bob Arum again in life, and Pacquiao is Bob Arum's fighter," Mayweather told FightHype.

What has changed since then? With Pacquiao having recently penned an extension with Top Rank until 2016, Arum is going nowhere. Unless Mayweather plans to sit down directly with Pacquiao as they did in 2012, he may have to swallow his pride.

Will there be a round five?

There is little doubt that even at 37 and 36 respectively, there is huge demand for Mayweather v Pacquiao. But while there has been a breakthrough in the stalemate between the two camps in recent weeks, old animosities linger.