The Serie A leaders are 3-0 up on their Scottish visitors ahead of the second leg in Turin, and the 31-year-old centre-back believes the whole team's defensive work has been the catalyst for them to perform well in recent years.
"The basis of our defence is organisation. We have been working hard even in the few days we've had [since the Napoli match]," Barzagli told reporters.
"There is a great harmony in this group. The midfielders and attackers also give us defenders a big hand.
"We are a compact team that works hard. We have a solid foundation and we hope that continues to be the case."
The former Palermo defender has been at the heart of Antonio Conte's defence since the start of the season, but he refused to speculate as to if this was his best campaign to date.
"It is difficult for me to say if this has been my best season or not. Of course, the important thing is continuity," Barzagli added.
"I am part of a solid defence that has been doing some great things for the past 18 months now."