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Ali lost his last world heavyweight title fight, to Larry Holmes in Las Vegas in 1980. The same fate had befallen Sugar Ray, the greatest of all world middleweight champions beaten in the same city almost 20 years earlier by Gene Fullmer.
The bigger they are, the harder they fall. When it comes to last international appearances, the sporting gods have a habit of playing fast and loose with those making their last stand.
Bradman, acknowledged by historians as head and shoulders above every other batsman in Test cricket, took guard against England at The Oval in 1948 needing just four runs to finish with a Test average of exactly 100. Instead, on his last match, he was bowled second ball for a duck.
Best, a footballing Michelangelo if ever there was one, deserved to leave the international stage on a more august occasion than a losing World Cup qualifier in Belfast, even if nobody realised at the time that they had seen the last of him in the green of Northern Ireland.
As for Gretzky, ice hockey superstar supreme, he bowed out of the World Cup in the 1996 final as one of the Canadian team beaten by the USA in Montreal. To know when to retire is one thing, to leave them laughing, in the finest showbiz tradition, something else entirely.
It takes physical and mental strength on a monumental scale and, in a team sport, the quality of those around you, plus a fair bit of luck, like a French forward touching down in the final moments of the final match only to be denied because another French forward threw the pass forward.
The RBS 6 Nations can be fiendishly difficult to win as Ireland know better than most, a steeplechase akin to five times round the Grand National course at Aintree in fair weather and foul.
The famous old Championship gives nothing away. If ever one individual deserved to leave with the big prize, Ireland's perennial No.13 did but he would have to earn it the hard way - no favours and most definitely no freebies.
As he rides off into a golden sunset with the gleaming RBS 6 Nations trophy hitched to the saddle, Brian O'Driscoll leaves behind records which appear to be almost as untouchable as Bradman's.
England's Martin Johnson and the wonderful Wallaby John Eales may have finished up holding the World Cup but neither can match O'Driscoll for sheer endurance.
Both second row forwards lasted a long time at the highest level but not as long as O'Driscoll. His international career spanned 15 years, from 20 to 35 and now, after 141 Tests it is over, at least as far as the Ireland national team is concerned.
His total of 65 matches in the Six Nations, every one made in the starting XV as opposed to via the bench, is unlikely to be surpassed. Equalling it would take 13 seasons without missing a single match.
George North, more than 40 Tests to his name and still 21, could give it a go. With 16 Championship appearances behind him, he would need another 50.
Given the physical ferocity of the game, ten years without missing a single match is an improbably tall order, even for the mountainous Welshman.
Ireland's second RBS 6 Nations title, five years after rounding off their Grand Slam epic in Cardiff, provided more than a storybook ending for the best European player of the post-professional era. It brought another gripping tournament to a thunderous climax.
Wales may have been counted out of the title reckoning by England at Twickenham the previous week but the outgoing champions signed off in some style.
Seven tries overwhelmed Scotland as the Welsh made them pay dearly for Stuart Hogg's red card after 23 minutes to the tune of 51-3 - an RBS 6 Nations record for both countries.
By then, England, done and dusted after rattling up another half century in Rome, could only stand and wait for the denouement in Paris.
Even before kick-off at the Stade de France, England's fate bore an uncanny resemblance to Ireland's in the same city at the same stage of the tournament seven years earlier.
It would also end with the same result. O'Driscoll would have known exactly how the England players felt because, on St Patrick's Day 2007, his Irish team were also in Rome.
They, too, had topped 50 in beating Italy in the early match that day which meant France had to beat Scotland in Paris by 24 points to pick the title out of Irish pockets.
England won by 45 points when the margin had to be 50-plus if they were to set Ireland any target beyond a win by the narrowest margin.
As it turned out, Chris Robshaw's team finished two tries short of matching the Irish on points-difference as well as their try-count over the Championship, 16.
Back at their hotel in Rome seven years before, Ireland had to endure the anguish of watching a French substitute called Elvis, as in Vermeulen, win the title for France with a try 39 seconds after the clock had turned red. Just like last weekend, that, too, went to the TMO.
England awaited their fate not far from St Peter's Square in the splendour of the eighth century Complesso Monumentale Di Santo Spirito.
Goodness knows what was going through the minds of the four Irish players in Paris who had been in England's place in 2007 - O'Driscoll, Gordon D'Arcy, Andrew Trimble and Rory Best.
Once again their fate fell into the hands of the TMO, former international referee Gareth Simmonds from Wales and his verdict on the legality or otherwise of Damien Chouly's 'try'.
The scoring pass had, as all France must have feared, gone forward. England's last hope went with it and no sooner had Paul O'Connell collected the trophy than the runners-up were sending their immediate congratulations.
Head coach Stuart Lancaster will have won legions of new admirers beyond Red Rose country for his gracious reaction to losing the title by a whisker.
He paid generous tribute to Ireland as 'deserved winners' and spoke of 'a fitting finale and send-off for Brian O'Driscoll, a legend of the game whom everyone in this squad respects massively'.
But for an unfriendly bounce or two and Gael Fickou's sensational winner towards the end of the opening match in Paris, England's might have been celebrating a Grand Slam. For their young team, a near-miss will be an invaluable experience as they attempt to peak for the World Cup in 18 months' time.
They were not to know that, this time, the rugby gods decreed that it would be done differently - a title for head coach Joe Schmidt in his first RBS 6 Nations and a second in 15 Championships for a centre whose feats will be talked about for as long as the game is played.
My team of the Six Nations 2014:
15. Mike Brown (England)
14. Andrew Trimble (Ireland)
13. Brian O'Driscoll (Ireland)
12. Jamie Roberts (Wales)
11. Yoann Huget (France)
10. Jonathan Sexton (Ireland)
9. Danny Care (England)
1. Cian Healy (Ireland)
2. Rory Best (Ireland)
3. David Wilson (England)
4. Joe Launchbury (England)
5. Courtney Lawes (England)
6. Peter O'Mahony (Ireland)
7. Sam Warburton (Wales)
8. Jamie Heaslip (Ireland)