There is a saying that attack wins you games and defence wins you titles. It is perhaps the truest saying there ever was. Spain conceded only two goals in 7 games in the 2010 World Cup and Germany let only four goals in their World Cup-winning campaign in 2014.
In 2006, Italy conceded only twice as the campaign was solely based around a strong defence. So far in this tournament, Brazil have conceded only one goal and that was in their first game against Switzerland.
Thiago Silva and Miranda have formed an excellent centre-back pairing while Fagner has actually been a better right-back for Brazil than Danilo. Marcelo missed out against Mexico but was good in the matches that he played.
Even though he left his position often to attack, his zone was well covered by Casemiro (more on him later). And when Marcelo had to miss out against Mexico, Felipe Luis came in and filled the role beautifully.
This only shows how good Brazil are defensively.