Barcelona have a slight advantage after a 1-1 draw at Olympique Lyon, but they had to come back from a goal down.
Juninho put the home side ahead with a beautifully lofted free kick and it wasn’t until midway through the second half that Thierry Henrey headed home to earn Barca a draw.
Atlético Madrid, however, have a much tougher task ahead of them if they hope to continue in the competition.
Atlético were twice ahead in their game with Porto, first through Maxi Rodriguez and later following a speculative 25 yeard shot from Diego Forlan, but two goals from Lopez evened things out and Porto go into the second leg as favourites.