The improvement throughout the team at Chelsea has been remarkable this season, though the revolutionised defence is clearly the most impressive.
Antonio Conte's three-man backline and usage of wing-backs has seen Chelsea surge to the top of the table while riding a wave of clean sheets with just six goals conceded in the last 14 Premier League matches.
And yet defence remains an area of slight concern, largely due to questions over the strength in depth within the squad. On paper, the presence of John Terry, Kurt Zouma and Branislav Ivanovic should prompt reassurance. In reality, there are doubts over how much of a positive impact they will be able to have this season if called upon.
It is not a question of quality. Terry has been one of the best centre-backs of his generation anywhere in the world, Ivanovic has won everything there is to win in club football and Zouma has the ability and potential to become just as decorated as the other two. The issue here is mainly gathering form and fitness, something that is currently difficult for them to attain with a settled starting XI in place and no European or League Cup football in which to get some game time.
It must be something that Conte is also concerned about, considering his decision to recall Nathan Ake from his loan spell at Bournemouth. The move was made prior to Chelsea's 4-1 FA Cup win over Peterborough on Sunday though the understandably rusty performances from Terry and Zouma vindicated the manager's actions.
Conte clearly wants more alternatives at his disposal and including Ake in the first team squad as they push for the Premier League title represents both an intelligent and pragmatic option. The Dutchman has been at the club since 2011 so is familiar with his surroundings and will not need time bedding in. As a player already on the club's books there is also no fee to be paid. With other reported targets such as Southampton's Virgil van Dijk commanding price tags in the region of £60 million, the business argument is plain. As for form and fitness, Ake has started the last nine matches for Bournemouth and is already match sharp.
That Conte is choosing to place his faith in a youngster that has spent his developmental years at the club is an undoubtedly positive turn of events. The temptation to splash the cash must be huge with the Premier League title now a genuine target and yet the manager has gone against the grain of his predecessors and opted to reward youth. With Nathaniel Chalobah receiving more first team exposure this season, perhaps there is now genuine light at the end of the tunnel for those that climb through Chelsea's youth ranks rather than the dead end it had appeared to be.
For Ake, the move is double-edged. Having just established himself as a key member of Eddie Howe's impressive Bournemouth side, he now finds himself back at his parent club where he is likely to spend the majority of his time on the sidelines. On the other hand, the vote of confidence from Conte must also be encouraging and if he is to forge a senior career at Chelsea then this could be the moment it truly takes off.
Ake made his Chelsea debut as a 17-year-old but has led a peripatetic existence ever since with loan moves to Reading, Watford and Bournemouth. While not every young Chelsea prospect has prospered in such circumstances, he has made the most out his moves even if his impact has not always been instant.
He initially struggled to force his way into Quique Sanchez Flores' plans at Vicarage Road before making the left-back position his own. A similar situation then befell him at the start of this season at the Vitality Stadium. But following a home defeat to Sunderland in early November, he became an ever present at centre-back under Howe even chipping in with a few goals, including a dramatic injury time winner in a 4-3 victory over Liverpool. Having played in two different positions in each of the last two seasons, the 21-year-old's versatility is a valuable asset. Conte has stated that he sees him as cover for all three of the centre-back positions and is also interested in seeing whether he can provide an option at left wing-back. And yet none of these are his preferred position.
When Ake arrived at Chelsea almost six years ago, he did so as a defensive midfielder and actually hoped to establish himself in that role at Bournemouth. While he might yet become Chelsea's enforcer in the years to come, for now his destiny is in defence.