Back on September 24, with Chelsea having just been humiliated by Arsenal in a 3-0 defeat at the Emirates, Chelsea looked like a team well and truly in transition under new manager Antonio Conte.
Something had to change if the Blues were to get their season on track, and that's exactly what happened as Conte's deployed his favourite 3-4-3 formation.
The tactic has been used in Chelsea's past four league outings and it is fair to say it has produced some exceptional results.
Of course, it is easy to see that Chelsea have won their past four Premier League encounters since switching to the formation in the aftermath of the Arsenal defeat.
Wins against Hull City, Leicester City, Manchester United and, today, Southampton have seen the 2014/15 champions move to within one point of the league leaders.
However, it isn't only the 12 points accrued since deploying Gary Cahil, David Luiz and Cesar Azpilicueta as the last line of defence that should catch the eye.
That's because the west London club haven't conceded a single goal in the four games since making the formation switch as they've taken on the defensive identify seen in Conte's Juventus and Italy sides.
Given that Chelsea had conceded seven goals in the three games before their win at Hull City at the start of the month, it shows what a difference playing three at the back has made.
Oh, and if clean sheets aren't your thing, Eden Hazard and Diego Costa's goals this afternoon mean that the Blues have scored 11 goals themselves during the impressive run.
Conte's preference for a back three wasn't exactly a secret when he arrived at Chelsea this summer.
However, for the early weeks of the season the Italian manager simply didn't have enough fit defenders - or enough confidence in them - to utilise the tactic that had served him so well in Serie A and at Euro 2016.
The deadline day purchases of David Luiz and Marcos Alonso may have been labelled panic buys by some at the time. But, two months on, they have allowed Chelsea to take a crucial step towards becoming legitimate title challengers under Conte.