How do you know that Benfica will win in front of their fans? The second legs are always more interesting, but they're always played cautiously. Fenerbahce always knows how to perform in important matches, so i think it won't be easy for Benfica to beat them.
Unfortunately, we can't guarantee that Benfica will be able to achieve what they promise to do, but having the fans behind them certainly helps.
I've seen matches where fans cheered until the end, pumping up the team who then turned the result around in a few minutes.