The three playmakers
Perhaps the defining theme to Chelsea's season was the arrival of Eden Hazard and Oscar to complement Juan Mata, and in a broader sense, the shift towards a more technical, ‘modern' style of football.
Because of Oscar's involvement at the Olympics with Brazil, and with Victor Moses yet to sign from Wigan, Di Matteo was required to start either Ryan Bertrand or Ramires on the flank to complement Hazard and Mata. What might have been a forced move ended up being an effective one, with Bertrand/Ramires playing slightly deeper, and freeing up Mata and Hazard to combine on the opposite flank.
Oscar's first game came in the Champions League, against Juventus, which will long be remembered for a pair of stunning goals but was also significant for his deployment in a central position, instructed to man-mark the wily Andrea Pirlo, whose usual deep-playmaking craft was heavily restricted.
Surprisingly, in the following game against Stoke City Di Matteo chose to use all three of his exciting playmakers in tandem - Oscar centrally, and Mata and Hazard cutting inside from the flanks. It didn't seem to work against a defensive Stoke, but the Italian knew the new system would take time to become effective. "It certainly needs more work and practice to tactically integrate them perfectly into our system, but it's just a question of time, and them getting to know each other better."
But as I wrote after Di Matteo was sacked in November:
Chelsea continued to field the band of three, and a good run of form followed, with three impressive wins in their next three games, and they scored four in each one of those games. But the defensive vulnerabilities were clear: the full-backs were constantly undermined by a lack of defensive protection, and also by their instructions to provide width on the overlap higher up the pitch.
Rafa Benitez's solution was always obvious. He simply played with greater caution - with a pair of 0-0 draws at the start of his reign the perfect illustration of this - and although Chelsea played with more solidity, there was also far less of the integrated movement and clever football that was so entertaining under Di Matteo.
Gradually though, Benitez grew in boldness and reverted to the Oscar-Mata-Hazard trio, playing behind January signing Demba Ba. The major difference was that Oscar was always used out wide, with Mata continuing Benitez's love of no.10s by constantly remaining in a central playmaking position throughout his compatriot's reign.
Mourinho's return is interesting for a variety of reasons - particularly, how he uses the Oscar-Mata-Hazard trident will be fascinating to watch.
Ramires as versatile as ever
Chelsea's slender Brazilian is a very odd player. He doesn't fit neatly into the stereotype of flashy Brazilian footballers, and although he's remarkably versatile with fantastic all-round physical gifts, including the ability to run for days, he only seems to have one role in which he seems best suited to - as the box-to-box midfielder in a 4-3-3, a position which he suggested was his favourite in a recent Twitter Q&A.
But Chelsea have almost exclusively used 4-2-3-1 under Roberto Di Matteo and Rafa Benitez this season, meaning Ramires has been used in two specific roles - either as part of the midfield two, or on the right, as a more defensive option to complement Chelsea's creative players.
He's not particularly popular in either position for Chelsea fans - on the wing, it's thought that he's not technically talented enough to fit into Chelsea's "attacking" ethos, but many also feel his passing and technical ability isn't good enough for the demands of a pivot role - but regardless of how you judge his performances, his versatility has to be admired, and for that reason, he remains a key player in an unbalanced squad.
A return to 4-3-3 seems likely under Jose Mourinho, meaning Ramires will surely shift into his preferred role in the midfield, with the freedom to break forward, but Mourinho will certainly take advantage of his flexible nature.
Tangent: Without getting into too much speculative detail, it's interesting to note that one of Mourinho's patented moves at Real Madrid when chasing games was to shift Sami Khedira into an odd right-back role, where the German was instructed to basically defend the entire flank on his own while the rest of the side poured forward. It's not unfeasible with his energy and defensive contribution that Ramires could be used similarly.
A new centre-back partnership?
For years, John Terry was first-choice in the Chelsea back four, but this year, for both fitness and tactical reasons, he has lost his place under Rafa Benitez. He of course missed substantial time through injury when the Spaniard first arrived at Stamford Bridge, but he has been available for selection in recent weeks and been overlooked in favour of other options.
Instead, the role of the first-choice defender has fallen to David Luiz, who has ironed out the most significant wrinkles in his game - not to say he's now flawless - to emerge as one of the world's premier defenders. His aggressive, proactive style of defending is divisive - highly effective when it works, because it means Luiz wins the ball high up the pitch and closer to his own goal, but also highly ineffective when it fails, because it leaves his partner exposed.
Therefore, the identity of his partner is crucial. Surprisingly, Branislav Ivanovic emerged as Benitez's preferred option, complementing the Brazilian with his sheer physicality, as Raheem Sterling attests. "Ivanovic is the scariest defender I have played against," says the Liverpool winger. "He isn't dirty, he's just a tank. Big upper body, big lower body." The move back into the centre for Ivanovic also helped to accommodate the ever-improving Cesar Azpilicueta at right-back, where the Spaniard's positioning in attack is less erratic than the Serbian's.
However, It hasn't been all Ivanovic-Luiz. Gary Cahill has also played an important role, forming a partnership with Ivanovic when Benitez elected to push Luiz into midfield. Individually, Cahill is a very reactive defender, and is often the deepest of the defensive line - which helps explain his remarkable propensity for penalty box blocks, most notably in the final moments of the Europa League final.
Immediately before that block, Chelsea had taken the lead through Ivanovic's storming header deep into stoppage time - a fine reward for a strong season.
In the summer of 2012, Chelsea somehow went from having a squad possessing six strikers to just two - and with Daniel Sturridge fighting ongoing injury problems, often Fernando Torres was the club's only option up front.
One of the more interesting developments in Torres' game was his tendency to drift wide, and sometimes, deep into midfield. In broad terms, this was the opposite of how he played at Liverpool, where his role was very much about playing off the shoulder of the defence, using his pace to get in behind.
This evolution would partly be influenced by his struggles, but partly because it suited Chelsea's fluid attack. His drifting across the pitch - at times causing great consternation amongst Chelsea fans - created space for Chelsea's three playmakers to dart into, where they had an understated goalscoring impact. Of course, they are renowned for creating chances - but all three finished the season with highly respectable goal tallies. Mata, in particular, benefitted from the off-the-ball movement of Torres, and it's not radical to suggest Di Matteo wanted Torres to play like this, to give Chelsea that fluidity.
Torres was multi-faceted throughout the season, however, and sometimes stayed higher up, similar to his Liverpool style, which, when considering Demba Ba's natural positioning, seemed the specific instructions of Rafa Benitez. His best moments in the six months he was here - the goals against the Manchester clubs spring to mind - all came from chipped balls from Mata over the top of the defence. It shows not only how adaptable Mata's skills are in the final third, but how Chelsea could play in two broadly different ways with their two striking options.
Chelsea finished 2011-12 with a European trophy (and an FA Cup), thanks to a defensive, counter-attacking system that saw the wide players play important, disciplined roles, tracking back to form a second bank of four ahead of the defence. Mata shifted from a position on the flank into a permanent number 10 role, and was an important factor in the team's reliance on set pieces to score goals, which proved decisive. Sound familiar?
That's not to say we haven't evolved, but it merely shows that for all the talk of 'needing' to evolve to a more 'modern' style of football, there remains more than one way to win.