We've seen Pep Guardiola persist with an experiment to play three at the back in the past few weeks. Given the Blues continued trouble at the fullback position, Guardiola has put his faith recently in a three-man backline that often keeps natural-left back Alexsander Kolarov in the mix playing centrally.
On Saturday, Guardiola used a back three against a rather unambitious West Brom side that under Tony Pulis often plays negatively against top sides. But a 4-0 win away from home against anybody is significant especially when you consider how difficult a time the Blues have had keeping clean sheets or limiting comical defensive errors.
A key to plying a three man back-line might be having both Fernando and Fernandinho on the pitch at the same time shielding the back three. Fernando remains a ball-winner of massive quality despite the fact that his ball-playing skills may not match the Guardiola style. Fernandinho has an uncanny knack of tracking runners in open play who advance from deeper-lying positions in the midfield. Among the contributions Fernandinho makes, one of the least appreciated is his reading of the game when the Blues are playing without the ball.
The back three seems a good idea given the limitations of the Blues fullbacks and the ability to play the likes of a Fernando to shield the backline. I'd expect it to continue going forward.