"Obviously we are very disappointed, as 2-0 at home is a difficult result. Unfortunately it went this way, but we have another game to play and must go there trying to score at least two," said the midfielder.
"We had problems because United tried to keep possession and switch places often. I thought we were very unlucky, as we took the game to them and conceded on the only real chances Manchester had."
The second leg is at Old Trafford in eight days, though Aquilani refuses to concede defeat.
"I think we must never say it's over as that is not right. Undoubtedly it's very difficult, but we have another match at our disposal and need to give it our best."
With Francesco Totti injured and Simone Perrotta suspended, Aquilani was pushed further up into the support trident in a new test for him.
"I have always said I prefer playing in a deeper role, as I tend to find myself with my back to goal and I'm not all that quick at turning. I can play this position, but it didn't go well tonight."