Two early goals for United took the edge off the all-English clash, which nevertheless dominated the evening's viewing with a 32% share and peaked with 9m viewers.
But the audience fell short of ITV1's average ratings for last year's semi-finals -- 10.2m for the first leg game between Liverpool and Chelsea and 8.6m for the second leg game between Manchester United and Barcelona.
ITV was also unlucky with its other semi-final this year, Chelsea's 0-0 draw at Barcelona drawing in just 6.4m.
Out of the other channels at 9pm-10pm BBC One scored highest with 4m tuning in to see the conclusion of drama series 'All The Small Things'.
Channel 4 took half of BBC One's 16% share with a documentary on children with disabilities, 'Born To Be Different: Turning Nine'. The programme brought in 1.7m viewers.
Five's 'CSI' attracted an 11% share with 2.6m viewers, while BBC Two offered 'How Britain Got The Gardening Bug' at 8.30pm-10pm, garnering 1.6m viewers and a 7% share.