Porto stunned the home fans by taking the lead inside four minutes.

United defender Jonny Evans was at fault, sending a poor clearance straight to Cristian Rodriguez who ghosted round the Ireland international before curling a smart left-foot shot beyond Edwin van der Sar into the bottom corner.

Few realised at the time but it was a sign of things to come with the visitors continuing to dominate a United side looking short of pace and laboured in midfield.

Photographs: Reuters