Most tactical reviews of Chelsea’s season would be a few sentences long. The Blues, we’re told, started out the season by playing free-flowing, attacking football before blithely slipping into more prosaic bus-marking to secure the title in the second half. Which, broadly speaking, isn’t untrue. But it’s hardly tells the whole story.

The two Chelseas — bus-parking monsters to close the season, angelic attackers to start — were not markedly different, something that becomes obvious when their defensive record in the second half is examined. For a supposedly defensive side, the Blues were startlingly weak for most of the stretch run, being pegged by after taking the lead no fewer than 12 times in all competitions after January 1st.

That’s not a Mourinho-like record, and aside from a handful of matches in which a deliberately defensive side was put out (which mostly involved fielding Kurt Zouma as a midfielder) it’s difficult to see any wholesale changes from first to second-half Chelsea. Instead, it’s probably best to look at them as a more and less effective version of the same team; an attack-first side that was surprisingly vulnerable to being pegged back by anyone who could apply sustained pressure.

So how do Chelsea play? Against most teams the Blues line up in a standard-looking 4-2-3-1, with a central midfield of Nemanja Matic and Cesc Fabregas and Oscar ahead of them. But since this is Jose Mourinho we’re talking about, there are a few unorthodox tweaks to look at. The two most important are the positions of the fullbacks and the role of Oscar at number ten.

Oscar

He’s often reviled for his supposed lack of production, but that’s mostly because of the unorthodox take he has on his position. The trequartista tends to be seen as a creative attacking force, but Oscar, while capable of doing damage (his assists for Diego Costa against Newcastle and Eden Hazard versus Manchester United were both sublime, and he scored one of the goals of the season against QPR), prefers to play in a more supporting role.

At their best, Chelsea’s forwards are a freewheeling chaotic force, and it’s Oscar who has to read them and take up positions where he can reinforce the attack without compromising the Blues’ defensive shape on the counterattacks. That often means he has to stay deeper than a more traditional number ten, but that doesn’t mean he’s not doing his job. Oscar flows naturally to where Chelsea need him, and with the likes of Hazard, Costa and Fabregas his balancing act sees him mostly in the shadows, putting in a defensive shift while everyone else is attempting to bomb forward.

It’s an usual way to play an attacking midfielder, and it results the Brazilian getting nowhere near the credit he deserves. But when he’s gone, you can tell. Chelsea are rarely near their best without Oscar on the pitch, and the disaster against Paris Saint-Germain probably would never have come to pass had he not been pulled off at halftime.

The Fullbacks

Modern fullback play is simple and simplistic,. One might argue that their job revolves around crossing — fire in as many as possible on the overlap and prevent the opposition doing the same. The more progressive managers, however, appear to see fullbacks in a different light. Pep Guardiola notoriously uses his as auxiliary central midfielders in order to hold possession while the rest of the team’s been pushed up, and while Mourinho isn’t quite that idolatrous neither Branislav Ivanovic nor Cesar Azpilicueta play as one might expect.

On the left, Azpilicueta’s role is primarily defensive. Hazard is left to do much of the attacking, and Azpilicueta mostly goes forward as a cross-field switching option rather than as a regular overlap. This allows him to both get away with being a right-footed left back (he doesn’t have to whip the ball in on the run very often) and also cuts the space he has to defend, leaving one of the game’s best one-on-one tacklers with a major advantage against his direct opponents.

The other flank is a completely different story. Ivanovic’s position is ludicrously aggressive, which allows Willian to come inside and support the other midfielders. Instead of being a crossing option, Ivanovic’s main attacking function is to assault the opposition with something very much like blunt force trauma, staving in their left side and allowing the Blues to flood the box with bodies. But Ivanovic has nobody behind him to cover, and the decision to play him so high up the pitch leads to a structural weakness in the channel between his nominal position and right centre back Gary Cahill.

The Attack

Ivanovic’s play is one of the three pillars of Chelsea’s attack. The other two should be obvious: Fabregas and his passing is the team’s route through the middle, and Hazard’s absurd dribbling ability is used to disrupt opposition defences and let his teammates take advantage of the chaos.

Hazard is the Blues’ most potent weapon. His dribbling ability is unmatched in the league, and when he goes on runs he tends to leave a trail of bodies in his wake. Defenders love to swarm him, but he’s good enough to take advantage of that and squeeze the ball to a free player even in tight situations, giving Chelsea the chance to strike will the opponent is unbalanced.

Fabregas is a more orthodox player. His ability to pass from deep — he especially loves looking for Diego Costa on the counterattack — is probably unmatched in the Premier League, and at times he can seem completely unstoppable. He’s not just capable on the break, however, and is an important part of the Blues’ buildup play, especially when the other attacking players occupy the defence and let him drop deeper in order to pick out passes.

The three different routes Chelsea use to get to goal mean that it’s very difficult to stop their overall threat. Placing someone on Fabregas merely means that there’s one fewer man for Hazard to beat, and Ivanovic is going to be a brute-force danger on the right even if you lined the pitch with barbed wire and trenches. With Costa finishing whatever those behind him can provide as well as the set piece threat the Blues can offer, they’re very difficult to stop.

The Defence

Chelsea play a medium block rather than the stereotypical very low one, but avoid having John Terry and Gary Cahill caught out with quick passes by applying a heavy press with their attacking midfielders and centre forward. Oscar’s importance is obvious here, as is Willian’s and Hazard’s, but Diego Costa’s contribution to Chelsea’s defensive game has gone virtually unnoted. It’s probably instructive to watch the games he missed due to injury — against Manchester United at Old Trafford in particular the Blues were unable to apply pressure at the source and were thus on the back foot for far more of the match than they would have liked.

The defence is exceptionally solid barring transition attacks down the right, which are inevitably dangerous when your right back lives so high up the pitch. Once their shape is reset, Ivanovic and Cahill form a far better combination than generally allowed, and teams tend to prefer attacking Azpilicueta in the air with crosses from right rather than going for Ivanovic directly, although he’s beatable on the ground once overloaded.

There is a reason, however, that this Chelsea side is so much more vulnerable to conceding sloppy goals than in Jose Mourinho’s first spell at the club. The central midfield is exceptionally porous. Fabregas works hard, but his positional play is virtually non-existent and he spent most of the first few months of last season chasing players everywhere. Matic is, of course, a more stable presence, but it’s difficult to call him a pure defensive midfielder when we’ve seen the likes of Claude Makelele at the club. He too can be drawn into chasing the ball around, and opposing teams spend much of their time attempting to lure both midfielders over to one side in order to bypass them entirely with a switch of play.

Without a midfield screen, Terry and Cahill are vulnerable, and said screen is surprisingly easy to hit when either of the central players loses concentration.

Alternatives

Chelsea have a difficult time playing in anything but their usual style when in their first-choice XI and shape, and the ‘defensive’ switch around January mostly involved being more conservative with Ivanovic’s position, which left ground for everyone else to cover and thus reduced the crazy spaces of earlier days. When Mourinho wants to play more defensively, he’s so far favoured dropping Oscar and moving Fabregas into the hole behind the striker. Sometimes Ramires is enlisted to give Chelsea a 4-3-3 feel, at other times we get John Obi Mikel. And during injury crises, Kurt Zouma has been known to show up as some sort of terrifying midfield smash-tank.

These changes have a fundamental impact on how Chelsea play, significantly reinforcing the defence at the expense of the attack. Without Oscar (and with Fabregas higher up the pitch and Ivanovic deeper), the Blues are far more reliant on Hazard to open up defences on his own or hitting the opposition with set plays. They’re also less capable of pressing with Oscar out, which allows top teams to dominate possession and wear us down.

This is Fabregas’s midfield, for better or worse. When he’s on form, he’s able to crush weaker sides that have historically given us problems, but the gymnastics Mourinho has to do to fit him in against stronger opposition played a major part in our relatively unimpressive record against top sides. Chelsea simply have no credible alternative to Fabregas at present, and thus will once again have difficulty in keeping possession against top sides without compromising their defensive alignment.

Expectations

More of the same. Chelsea were a success last year, despite the disappointment of being knocked out of Europe by David Luiz and Paris Saint-Germain, and the squad hasn’t been significantly changed. The incomings and outgoings have all been for reserve positions rather than for starters, so we shouldn’t be anticipating any major changes in playing style. Perhaps we’ll see Ivanovic start to slow down, but other than the Serbian Chelsea’s most dynamic players are all young enough to be improving. Barring a surprise buy in the summer, this squad will look and play mostly like it did last year.