Pep Guardiola believes cutting out the "stupid mistakes" in defence has been the key to Manchester City's upturn in form.
Since a surprise 5-2 thrashing by Leicester in September, City have conceded just nine goals and kept 14 clean sheets in 22 games in all competitions.
That has helped City recover from an indifferent start to the campaign in which they dropped points in five of their opening eight Premier League games.
The key to their revival at the back has been the form of summer signing Ruben Dias and a revitalised John Stones, who have formed a strong partnership.
Manager Guardiola, whose side host Championship Birmingham in the FA Cup third round this weekend, said: "Except the game against Leicester when we were so naive, (conceding) three penalties unnecessarily, in the rest of the games it was really good how solid we were, how (few) chances we conceded.
"We cannot deny that lately the back four is so solid. It is a big help for everyone, and everyone has helped incredibly.
"The back four don't make stupid mistakes. Even one against one, blocking shots like Ruben or Stones – they were brilliant.
"Everyone is so committed and involved and that helps us. It is important to maintain in most of the games zero in our goal, because we know from the quality we have, especially in the middle, we are able to create chances to score goals."
City had numerous problems in the centre-back positions last season with Aymeric Laporte injured and Guardiola appearing to lose faith in Stones and Nicolas Otamendi, who has now left the club.
For most of the campaign Fernandinho was their strongest centre-half having been shifted from his preferred midfield position.
The Brazilian, with the added responsibility of the captaincy, has returned to a defensive midfield role this season and Guardiola feels he is thriving.
Guardiola said of the 35-year-old: "He's leading the team in an exceptional way in the good and, especially, bad moments.
"He's an example and when the team can take that example we will be stronger. I'm delighted for all our period together but especially in this season as captain.
"From the beginning of the season he made a step forward and showed how to adapt. I'm really impressed."
Fernandinho is again nearing the end of his contract having signed a one-year extension 12 months ago. It is not clear whether the player will further extend his stay but Guardiola does not seem to be against the idea.
He said: "With the players in this part of the season, everything is open – players who have contracts, players who are out of contract, players who want to leave.
"Like with managers, we have to win our positions or we'll be sacked. All I will say is I'm more than impressed with his role as captain."
