The Spaniard went down with minimal contact from Courtois. Troy Deeney duly converted to give Watford a half-time lead.
Speaking to Sky Sports after the game, Deulofeu said: "We are happy for these three points, the team fight at the beginning and we are worth this win. I'm so happy for my fist game at home.
On the penalty he won in the first half: "Daryl Janmaat gave me a good ball and I think it's a clear penalty. He (Thibaut Courtois) touched me.. I think."