The Belgian midfielder produced a late equaliser for Spurs which allowed them to edge Lyon 3-2 on aggregate in the Europa League Round of 32 and Villas-Boas was thrilled to see him lift the North Londoners into the next round after a poor first 45 minutes.
"We didn't play well in the first half," he admitted.
"In the second half we were the better team. We created some chances and we were rewarded with the second goal in the end. Individual players make a difference and Mousa certainly made the difference tonight."
On Dembele's goal he added: "It was good. When you score in the last minute, there are all sorts of emotions going through you, especially with a goal that brings you into the next round.
"We want to continue setting the example in this competition. Everyone is buzzing to continue in this competition which is why we reacted so fully, so joyfully in the end.
"If you count the number of opportunities Lyon had in both legs it would have been unfair for them to go through."