The Rojiblancos suffered a 1-0 defeat in Portugal, with Eliaquim Mangala scoring the only goal of the game, but the 42-year-old coach says all is not lost.
Eliaquim Mangala scored the only goal of the game at the Estadio do Dragao to make the Portuguese side the favorite to reach the last four.
However, Emery says he saw enough in the first leg to convince him that Sevilla have every chance of turning the quarterfinal tie around at the Ramon Sanchez Pizjuan.
"We are optimistic we can do better and the tie is still open going into the return," the Rojiblancos boss told GoIT. "We knew the importance of standing firm, particularly early, and I thought we did well in that regard. Other than the goal, they did not cause us much danger.
"Right now we're at a disadvantage, but we have to feel more confident [at home] and find our best form.
"Moreover, we will have the fans with us."