The Bosnian came off the bench to score a late winner for City in their 2-1 Premier League victory over Spurs at the Etihad Stadium on Sunday.
"To have a player so strong of character like Dzeko to come on again in the final minutes when the team needs him and to respond like that is something that, for me, deserves great credit, and continues to surprise me," BBC Sport quotes Villas-Boas as saying.
"He continues to be left on the bench then come on and destroy teams.
"Dzeko in the end made the difference with his ambition to prove that he always deserves to be in City's starting XI."
Tottenham are seventh in the league table with 17 points from 11 matches.