Turnbull has stepped in for the injured Petr Cech.
He said: "I am always prepared mentally for a moment like this, which you have to be. I am always ready to come in when called upon.
"Yes, it is always very difficult [to come in all of a sudden].
"Before Everton, I hadn't played since the Wolves game [on September 25] and that is not easy, especially in the goalkeeping position where the more you play, the more confidence you have and the game then feels pretty natural.
"But it's been good to be involved again as it's been a long time. It's been good to play and pleasing to make a contribution."