Having watched Fiorentina struggle to break down their Portuguese opponents in the opening half hour, Montella was delighted with the way his side changed their approach to secure a 3-0 win.
Gonzalo Rodriguez opened the scoring before Ryder Matos and Giuseppe Rossi sealed the Group E victory in the second half in Florence.
Fiorentina's win leaves them favourites to win the group, but Montella is not getting too carried away after one result.
"I take things one step at a time. I don’t want to dream, as I am a very realistic person," he told Mediaset.
"Before the goal we did things wrong, while after breaking the deadlock we played fine football, even if towards half-time we allowed Pacos too much space.
"The team then showed how practical it was to finish off the match."
Rossi's 76th-minute strike was his fourth goal in as many games this season, but it was midfielder Borja Valero who came in for special praise from Montella.
Valero created Matos' goal - his first for the club - just after the hour and his overall performance really pleased the 39-year-old.
"I think he (Valero) is so intelligent that he knows how to rest during a game," he added. "His training sessions are matches, because he manages to light up so much better in a game situation than in training."
