Ferguson has already won 48 trophies in his career and is expected to land at least one more this season as his side stand 12 points clear of Manchester City in the Barclays Premier League.
By contrast, Mourinho, who will be in the opposing dugout on Wednesday when United take on Madrid in a mouthwatering Champions League clash, has a comparatively measly 20 to his name.
However, in pledging to extend his career into his 70s, as Ferguson has done, Mourinho has given himself another two decades to scoop silverware.
And if the Portuguese coach enjoys such longevity, Ferguson is convinced his friend will eclipse his own achievements.
"It is very possible that Mourinho will finish as the most successful manager ever," said Ferguson. "It depends where his future lies.
"How long he will be at Madrid for a start because they would always give him the opportunity to win major trophies."
Mourinho has already done something Ferguson is unlikely to match; winning the Champions League with different clubs.
"If he does it again he will be the first to do it with three," said Ferguson.
"He has won the Treble with Inter Milan. He has won a lot of trophies for a young man.
"He has 20 years to catch me up so it's possible he could beat my record."
Ferguson is adamant he will not still be ploughing on in 20 years, as Mourinho suggested.
Yet there is no doubt the Scot is stimulated by the challenge provided on the domestic front by Manchester City, just as he was when Mourinho arrived at Chelsea in 2004.
"He transformed Chelsea," said Ferguson. "They got off to a flying start and caught us on the hop.
"We were chasing their tail for two years."
They also had the Indian sign over United.
Indeed, excluding a penalty shoot-out win in the 2007 Community Shield, Ferguson has only enjoyed two victories in 14 meetings with Mourinho.
"It doesn't bother me that he has a better head-to-head record," he said.
"You can't beat them all. I'm happy with my own record."
For all their battles, Mourinho can count Ferguson as a friend.
The pair met immediately before Manchester United's victory over Everton on Sunday and after serving Ferguson with wine even he admitted was awful when he first arrived at Chelsea, it is a fair bet Mourinho will come up with something better for their post-game chat on Wednesday.
The stakes are high, though. Time is not on Ferguson's side as he looks to secure another European accolade, whilst after a desperate campaign on the domestic front, Mourinho has to win if he is to convince anyone he can stay in his job.
"Real got off to a shaky start and Barca came out flying," said Ferguson.
"It was like when Chelsea got off to those flying starts and we couldn't catch them.
"But I watched their game against Barca the other night - there wasn't a lot in it.
"Ronaldo is the one I worry about but you can't dismiss Real Madrid have a good team."
The respective league tables suggests both sides' strength lies in attack rather than defence.
That knowledge allowed Ferguson to make a bold prediction.
"It won't be 0-0," he said. "I can assure you of that.
"It can live up to expectation.
"History always plays a part in these types of the games and the two teams' desires to go forward ensures there will be goals."