At the start of the season, few would have expected Liverpool v Chelsea, coming so close to the end of the season, to be a title decider - but then again, few would have expected it to be overshadowed by Jose Mourinho's threats of fielding a weakened side as he prioritises a Champions League semi-final.
The success of Brendan Rodgers' side has largely been predicated on the outstanding goalscoring form of Luis Suarez and Daniel Sturridge, and it is the latter whose return from injury causes the only real dilemma in Liverpool's team selection. Jordan Henderson is, of course, suspended for the red card picked up by a reckless challenge in the dying moments of the match against Manchester City, and will be replaced by Joe Allen filling in that right-of-centre midfield position, as he did against Norwich.
The key to this match, and what makes it particularly fascinating, is how the rest of the side will be setup. Rodgers' constant tinkering has caught opponents by surprise, and he's used a variety of formations this season - from 4-4-2, 4-2-3-1, 4-3-3, 3-5-2, 4-4-2 diamond and most recently, a 4-3-2-1.
That last one would be the safest bet for what formation he will opt for against Chelsea seeing as it featured against Norwich but it effectively comes down to whether Sturridge starts - which would predicate either the diamond or the 4-3-3.
Regardless of formation, Liverpool's approach remains constant. They work the ball out from the back, with Steven Gerrard's redeployment as a holding midfielder the catalyst for their transition from defence to attack. He drops between the centre-backs and works the ball forward quickly, both with short passes to the midfielders near him or longer balls towards the attackers - his through balls for Sturridge's runs off the shoulder are particularly effective, as demonstrated by the latter's goal against Sunderland.
Because Norwich used a diamond formation from the start, Liverpool found it very easy to play out through the full-backs, with Glen Johnson enjoying lots of freedom down the right-hand side. When Neil Adams switched to 4-5-1, Liverpool suddenly came under lots of pressure - with natural width, Norwich could prevent the out-balls to the full-backs, and press higher up, closing down the centre-backs and forcing them into sloppy forward passes.
The reason why Liverpool stick to playing out from the back, however, is because when they bypass the opposition press, it creates lots of space in front of the opposition defence for the attackers to drive into. Ultimately, this is where Liverpool's strengths lie - getting their quick, agile attackers on the ball high up the pitch, and giving them space to drive into both on the counter-attack and longer periods of possession. When the counter isn't on, Liverpool almost deliberately start building from deep positions, as if to invite opponents onto them, inevitably creating space higher up for the likes of Sturridge, Suarez and Raheem Sterling.
This contrasts neatly with the more methodical approach favoured by Rodgers at Swansea, and demonstrates the adaption of his approach to the players at his disposal. Liverpool aren't a purely counter-attacking side, but their greatest attribute is the speed and directness of which they attack.
The freedom of Suarez and Sturridge (and to a lesser extent, Sterling) to be in these kind of spaces is linked to the fact Rodgers' formations give those players the freedom to ‘cheat' in the defensive phase, something that is particularly obvious in the 4-3-3. They stay high up, free of defensive responsibility, which leaves Liverpool undermanned in wide areas - while Johnson and Jon Flanagan are good in 1v1s, it's an area where Chelsea will feel confident they can exploit, particularly with overlapping players.
It's risk management, though. The obvious counter-effect of freeing up Suarez and Sturridge from defensive responsibility is that they are in positions to counter-attack, and when the ball is turned over, they can both run directly at opposition centre-backs. Therefore, while Chelsea's full-backs could get forward to expose Liverpool's full-backs 2v1, that leaves their own defence exposed to 2v2s against Suarez and Sturridge.
The partnership of Suarez and Sturridge upfront is deadly. It's strength comes from its unpredictability, and the anarchy of both players: guided by intuition, but still synchronised. Both drift towards wider areas to pick up possession and take players on, but also narrower to the edge of the penalty box to attempt curled shots (with Sturridge often dropping to the right corner of the penalty box to cut inside and shoot on his left). If one goes wide, the other stays central - and if they're both central, they can feed each other in behind, often with Suarez playing the more creative role.
Manchester City's response to this was to keep Pablo Zabaleta and Gael Clichy from moving forward, effectively keeping a 4v2 at the back, which had a nullifying effect on the front two but opened up space elsewhere, and Mourinho will likely do the same, just as he did midweek against Atletico Madrid.
The fact that Rodgers has so many tactical options at his disposal gives him an advantage over Mourinho - even after naming the starting XI he can hide the formation he will play, and it's tough to predict what formation he will use here. If Sturridge is fit to start, the diamond seems likely as to pack the midfield - perhaps even with Joe Allen and Lucas Leiva beside Gerrard, to give the holding midfielder support against Chelsea's attacking midfielders. If Sturridge doesn't start, however, the Christmas Tree or 4-3-3 seem more likely.
Regardless of Rodgers' formation, Mourinho will likely take a cautious approach to this game - using Nemanja Matic perhaps in tandem with John Obi Mikel or Frank Lampard (who are both suspended for the midweek Champions League tie, so likely to feature here) to shield the defence, which will help to nullify Sterling's dangerous running. Originally emerging as a tricky winger, the youngster's recently starred as a direct no.10, starting central but moving wide and constantly charging forward with the ball, exploiting the lack of protection in front of City's defence created by their use of Yaya Toure and Fernandinho in tandem.
The problem was compounded by Rodgers' use of Phillipe Coutinho to the left of his midfield diamond, because Fernandinho was torn between protecting the defence from Sterling's runs, or moving forward to press Coutinho and prevent him from slipping through balls in behind, the Brazilian's most dangerous attribute.
Against Norwich, Coutinho was used in a more advanced role on the left of something approach the Christmas Tree formation, although Sterling was tucked in quite central and thus offered Johnson very little protection (as aforementioned). That created a neat left-sided triangle from where Liverpool's three attackers could constantly combine, with Coutinho teeing up Sterling for the opening goal and then the goalscorer turning provider for Suarez a few minutes later.
Those two goals added to Liverpool's already impressive first half record. They've scored more goals in that period than any other side in the league this year, partly because of the atmosphere generated at Anfield. Chelsea should be very cautious in the opening twenty minutes, looking to stem Liverpool's inevitably fast-paced start, before gradually attacking Liverpool more as the game progresses.
In two consecutive weeks, for example, Liverpool have looked particularly vulnerable in the second half, seemingly unable to maintain the high tempo but also uncomfortable soaking up pressure for long periods, with the defensive instabilities created by their attacking approach coming to the fore as opponents grow into games.
While Martin Skrtel is more of a ‘penalty-box defender', it's amazing how much he seems to struggle with opposition strikers inside the area, often resorting to ludicrously physical measures (particularly at set-pieces) that have somehow escape the attention of officials. Daniel Agger may start instead. Furthermore, Simon Mignolet's struggles at defending crosses were obvious at Norwich and this could be an area Chelsea may target with Demba Ba likely to start upfront.
Going forward, the Manchester City match was a good example of how Chelsea can attack Liverpool, as they created chances through the lateral movement of David Silva from a central role. This was particularly effective when James Milner came on in the second half, combining neatly with the Spaniard down the right to overload Jon Flanagan, continually get into positions to cross from the by-line, creating City's equaliser with a fine cut-back. The secondary effect of Silva's movement was that it caused real problems for Gerrard as the lone holding midfielder, because he was dragged around by Silva's drifting.
Again, it's risk-management by Rodgers. He gets the benefit of Gerrard's passing when Liverpool have in possession, but loses defensive solidity by deploying him in this role.
To summarise, then, Liverpool's system has a lopsided balance. They sacrifice defensive solidity for attacking firepower, which is why they can storm past weaker opposition, but could be vulnerable to strong opposition like Chelsea - who are capable of soaking up pressure and then breaking quickly.