It was a night of comebacks and mini-comebacks at Old Trafford. Roma who had to make three first half subs due to injury came from a goal down to take the lead through Lorenzo Pellegrini and Edin Dzeko after Bruno Fernandes had put the host ahead.
Edison Cavani equalised shortly after the second half began to draw United level and added another minutes later to put United ahead. Bruno Fernandes, Paul Pogba and Mason Greenwood added salt to the injury to make it 6-2.
Villareal led by Arsenal’s former manager Unai raced into an early lead against Arsenal, Manuel Trigueros opened the scoring in the fifth minute and Raul Albiol added the second in the 29th minute.
Arsenal were reduced to 10 men early in the second half after Dani Ceballos was sent off for a second bookable offence. Nicolas Pepe pulled one back for the Gunners from the penalty spot after Bukayo Saka was tripped. Etienne Capoue was red carded later on which means both teams finished with 10 men.
The second legs will be played in Rome and London on May 6 as Arsenal and Manchester United will be looking to set up an all English final like 2019 when Chelsea beat Arsenal 4-1.