Duran struck on 79 minutes to earn Villa the 2-1 win on Saturday.
Emery later said, "A very difficult place. Today we deserve it but it was a very tough match. Our game plan was progressively getting better in 90 minutes. I think now the first match after pre-season some players are not fit to play 90 minutes. I think today their attitude, commitment was fantastic.
"The idea is to try to have players in the bench as well with the qualities played in the starting 11. This year we are improving our level facing the Champions League. Of course we want to keep the same position competing the way we did last year and we have to be very demanding with our players. We are ready to play the next match at home against Arsenal on Saturday and we showed a little bit the different possibilities in the squad. The impact of Jhon Duran was very important because he still wasn't fit to play 90 minutes, Ollie Watkins."
On Duran, he added: "We believe in him and he has to play, he has to be ready to train every day like he was doing the last week and like he trained today. For me we need two strikers and both have to have good performances and good commitment to play like they both played today."