Sousa's side replaced Inter atop the table after Nikola Kalinic inspired Fiorentina to a 4-1 victory over Roberto Mancini's team on Sunday.
Kalinic netted a hat-trick as La Viola leapfrogged Inter on goal difference after six matches.
The likes of Inter, Roma and reigning champions Juventus remain favourites to lift the title come May, having invested heavily during the off-season.
Speaking to Sky Sport Italia, however, Sousa insisted his ambitious Fiorentina outfit will fight for Serie A.
"Football is like this in Latin countries, it goes from zero to 80," Sousa said.
"I already said there were other teams who invested heavily for that, but I won't hold back either, as we have the quality to face every match knowing we can win.
"I told the lads from the start I want a team always ready to take on anyone, always maintaining our approach.
"We have principles of football that we work hard on and as time goes on this will give us more confidence going forward."