Mourinho has won the League Cup in each of his three full seasons at Chelsea and a fourth triumph, this time with United, would create another first in the club's illustrious history.
The Reds will meet Claude Puel's Southampton side - themselves looking to re-write the record books.
"The Saints" have never won the League Cup trophy and their only other major honour came back in 1976 when they beat United in the FA Cup final as a Second Division side.
No Reds manager - not even legendary knights Sirs Matt and Alex - have been able to win a trophy in their first season at the helm.
Dave Sexton is the only United manager to get anywhere near silverware of any description in his first campaign.
Even then, it was only a Charity Shield (which doesn't really count anyway) in 1977, shared after a 0-0 draw with Liverpool in the days before penalty shootouts.
Busby, who would go on to win 13 trophies at Old Trafford, including five First Division titles and a European Cup, had to wait until his third campaign for silverware - the FA Cup in 1948.
Sir Alex, British football's most successful ever boss, similarly endured a difficult three seasons at the helm before the FA Cup win in 1990.
History suggests that he may not have survived beyond that season had we not won that - a success which laid the benchmark for the phenomenal silver-gathering juggernaut that followed.
Three years on, and seven since he took over in 1986, the first of thirteen Premier League titles arrived in 1993.
Louis van Gaal delivered a domestic trophy in his second season last term but Jose has the opportunity to eclipse them all.
Seven months into a four-year contract, Jose has taken us into the first of three possible finals this season with United the only English team fighting on all four fronts.
He's stamped his authority and identity on the squad far quicker than LVG ever did and, if the talk is true, he looks set to be offered an new contract in the summer.
With the first major silverware of the season on offer, United are bidding for a fifth League Cup triumph to move joint second on the all time list of the competition's winners (Chelsea and Villa have five apiece).
Sunday's showpiece is the first of the Mourinho era at Old Trafford, but it almost certainly will not be the last.