Under the guidance of interim manager Ruud van Nistelrooy, United finally achieved a breakthrough in the competition, following three consecutive draws under former manager Erik ten Hag.
Reflecting on the resounding win over City, Amorim admitted that this performance was "a dream way" to sign off. Yet, he emphasised that his approach at United would differ significantly.
United swiftly appointed Sporting Lisbon manager Ruben Amorim as his successor.
However, Manchester United, eager for an immediate replacement for the recently dismissed Erik ten Hag, issued an ultimatum: accept the job now or lose the opportunity. After careful consideration, Amorim ultimately chose to make the move.
Goals from Timo Werner and Pape Matar Sarr put the hosts in control in Round Four encounter in the capital.
Manchester's French midfielder Paul Pogba had a great match as he made four assists
The result leaves the 2017 champions United well-placed for next Thursday's second leg in Roma.
Manchester United were inspired by Portuguese midfielder Bruno Fernandes on Thursday night, as he has been doing ever since his arrival.
Arsenal on Saturday held Manchester United to a goalless draw at the Emirates Stadium after the Red Devils had suffered a shocking 2-1 defeat against Sheffield United midweek.
The result means Manchester City, who on Tuesday won 5-0 away to West Brom, are the new league leaders.
