By Phil McNulty Chief football writer at Etihad Stadium 4 Jan From the section Premier League Share this with Digg Facebook Google LinkedIn Reddit StumbleUpon Twitter Copy this link https://www.bbc.co.uk/sport/football/46754957 Read more about sharing. Manchester City demonstrated substance as well as style as they overcame Liverpool, the greatest threat to their hopes of retaining their Premier League title, on a night of searing tension.Pep Guardiola’s City side – who made history to win the league with 100 points last season – knew they would need to dig deep into their reserves to beat a Liverpool team arriving at Etihad Stadium on the back of a 20-game unbeaten start to the campaign.The purist flourishes that have become the hallmark of City’s style were set to one side for much of a frantic, intense encounter in favour doing the dirty work required to get the job done after Guardiola admitted himself that a failure to win would make their title task close to impossible.And while the headlines may go to goalscorers Sergio Aguero and Leroy Sane, City’s whole approach and their victory was built on the performance of their great unsung hero.For all the glittering array of riches assembled at City, Fernandinho…