"It was the first game, which is always the hardest, in a very tough group. Others are extremely easy, for example there are some with no champions in them at all," moaned Mou.
"Barcelona are not just the reigning champions, but also the team that plays the best football in Europe at the moment.
"Obviously they had their chances, but so did we. This is the kind of game where each side only has three or four chances and if you score them, then you win.
"The first half was very balanced and if you look at Barcelona's history, they always tend to dominate possession, but that wasn't the case with us.
"After the break they did have more of the ball, but we also had some great chances like [Davide] Santon who was hauled down to stop the goal. If he had got through, that would've been 1-0 and we're home free."
Mourinho insisted: "I think this was a wonderful game of football and people who say 0-0 is not interesting are just wrong.
"It's easier to create a new system in defence, but upfront is much more difficult. That takes a long time to develop the style that Barcelona have, but I am satisfied with the team's concentration."