The midfielder struck in the last seconds to take us through against Lyon in the Round of 32 at the Stade de Gerland.
We've come through serious tests at Lyon and Inter Milan by scoring at key times in both matches and we now travel to Basel's St Jakob Park next Thursday knowing we have to do the same again with our quarter-final the tie at 2-2 after the first leg.
The Swiss champions took control with goals from Valentin Stocker and Fabian Frei in the first half before we clawed ourselves back into it with Emmanuel Adebayor and Gylfi Sigurdsson on target.
"We didn’t start well, made a few mistakes and they played well," said Mousa.
"I’m disappointed about that but you could see how we came back.
"It could have been worse, but it’s still possible. We have to win in Basel and we’re fully confident we can do that."
Before that, we have a huge match in the Premier League on Sunday as Everton visit the Lane for a 2.05pm kick-off.
"You saw how we came back against Basel and if we play like that for the full 90 minutes, then not many teams can beat us at White Hart Lane," added Mousa.
"We know Everton are strong and always tough to play against but if we manage to get the win then it will show that we are mentally strong."