Holding a comfortable 3-0 aggregate lead from the first leg, United's position never looked to be in real threat but the hosts struggled to capitalise on their chances.
Wout Weghorst hit the post in the first half and United continued to be unable to convert in the early exchanges of the second half until a triple change on the hour mark.
Martial finally broke that deadlock after 73 minutes, with Fred then poking home from close range to add further gloss to the scoreline and secure a date against Newcastle United on February 23.
The 59-year-old is currently employed by Serie A club Roma, having joined in 2021 on a three-year contract.
There are reports that Mourinho is not entirely happy in the Italian capital, specifically regarding player attitudes and the club's financial limitations.
TOP STORY – BRAZIL TO MAKE SHOCK MOVE FOR MOURINHO
Brazilwill make a sensational swoop to make Jose Mourinho their new national team boss to replace the departed Tite, according to la Repubblica.
An intermediary of Brazil's national setup will fly into Italy to meet up with the Roma head coach – who has also been linked to the Portugal job – and begin negotiations face to face.
Brazil had been linked with Manchester City boss Pep Guardiola, having reportedly turned to super agent Jorge Mendes to aid their pursuit of a new head coach.
ROUND-UP
– Journalist Bruno Andrade claims Manchester United have "overtaken" Liverpool in the race to sign World Cup winner Enzo Fernandez from Benfica. United boss Erik ten Hag is willing the trigger his €120m release clause.
– Manchester United have commenced talks with PSV winger Cody Gakpo, reports The Daily Mirror. Gakpo netted three goals in three World Cup group games.
– Fabrizio Romano claims that Barcelona have no intention of selling midfielder Franck Kessie or full-back Hector Bellerin in January.
– Paris Saint-Germain are interested in Real Madrid winger Marco Asensio, reports SPORT. Arsenal have also been linked with the 26-year-old, while Ara claims Barcelona are monitoring the situation and may swoop.
– PSG are also interested in signing Manchester United's Brazilian midfielder Fred, claims The Sun. That is despite United recently triggering a 12-month extension on Fred's contract.
– Bayern Munich have added Leeds United's French goalkeeper Ilhan Meslier to their transfer targets, reports MediaFootMercato. Bayern are looking for cover the injured keeper Manuel Neuer.
