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Formation
Figure 1: Formations for Nordsjaelland vs. Chelsea.
4-2-3-1 vs. 4-2-3-1 is something we see all too often in modern football, and it normally leads to some quite boring games if the teams are evenly matched stylistically and on talent. Fortunately for Chelsea's sake, that wasn't the case here. With none of Nordsjaelland's attackers posing too much of a threat in front of goal, Roberto di Matteo was able to be very aggressive with his players, going without a dedicated defensive midfielder in order to deploy both Frank Lampard and Ramires in the centre of the pitch.
The right side of Chelsea's attack was particularly fluid, with both Juan Mata and Oscar happy to play wherever circumstances dictated, going flank to flank and dropping back into the midfield to collect the ball. Moses, out on the left, was a little bit more conservative, sticking to his flank throughout.
The hosts, as expected, were much more cautious, although they did make several runs forward with their fullbacks. Ultimately, they were playing for a draw, and it was up to Chelsea to break them down. Thanks to a late goal onslaught, that's exactly what happened.
Average position
The differences between Chelsea and Nordsjaelland on the attack are made clearest by the 'average position' chart supplied by Opta (and ESPN Soccernet, in this case):
Figure 2: 'Average position' for Nordsjaelland vs. Chelsea.
Before we dig in, a cautionary note: 'Average position' isn't actually a measure of where a player actually stood on the field for most of the match. Instead, it's the average of where a player was when there was a recorded event involving that player. Since most recorded events are passes, it actually ends up being a proxy for a team's attacking shape.
So what do we make of this? The first thing that jumps out is the disinclination of the Nordsjaelland midfield to go forwards. Their pivot remained fairly deep even when the Danes had the ball. This means two things. The first is that it's harder to sustain an attack. There was only one spell of serious pressure from the home side -- other than that attacks were snuffed out reasonably quickly. The second is that it was much harder for Chelsea to mount a serious counterattack through the middle, because there were generally plenty of bodies deep.
The second is that Nordsjaelland were just as aggressive with their fullback positioning as di Matteo. This makes sense for both teams -- Joshua John, the hosts' primary attacking threat, was ostensibly a winger but repeatedly cut inside, making room for an overlapping run from left back Patrick Mtiliga. A similar situation repeated itself on the Chelsea right, with a very aggressive Branislav Ivanovic surging into space left as Juan Mata did his roaming thing. As for the left... well, Ashley Cole will be Ashley Cole.
Pressing
Nordsjaelland are a team that plays out of the back, which is an attractive style of football when it works and not so nice when it doesn't. Chelsea exploited this mercilessly. While I don't have a nice, Guardian-style chalkboard on which to plot the location of passes and tackles, it's beyond telling that Oscar and Torres had for more tackles than the rest of the team combined (Oscar won the ball eight times as the 'playmaker').
Pressing is dangerous for both sides. Obviously, it can lead to possession being lost high up the pitch for the side with the ball, but as we saw against Arsenal, strong technical sides can exploit the fact that they're being pressed to draw the opposition out of shape and scythe through them. Pressing, which goes hand in hand with a high defensive line* also very difficult to do for long spells, and can tire teams out quickly.
*Which, one would have to imagine, is why the speedier David Luiz and Gary Cahill started instead of John Terry.
However, it worked fine for Chelsea in Copenhagen. Here's how the move for the opening goal began:
Figure 3: Nordsjaelland set up their own demise.
A Nordsjaelland free kick, in their own half (David Luiz had 'fouled' Morten Nordstrand with what actually looked to me like a perfectly reasonable challenge). There is absolutely no reason for the Danes to give up the ball from here.
Figure 4: Chelsea press for their opening goal.
Two passes later, Jores Okure has given the ball to central midfielder Enoch Adu. Again, despite Torres in attendance, there's no real threat. But look at what's going to happen if he does lose the ball here. There are six Chelsea players, including both pivot players, in advanced positions against just four Nordsjaelland players plus goalkeeper Jesper Hansen. Incredibly, Adu dallies on the ball for long enough for Torres to nick in and steal it. A pass to Frank Lampard and then Juan Mata and it's 1-0 Chelsea.
This wasn't the only instance of the Blues winning the ball very high up the pitch. Indeed, Oscar had a goal disallowed early in the second half following an even deeper turnover, and one of Torres' missed chances came after robbing the ball from a red shirt.
This won't work all the time -- Nordsjaelland were able to escape the press occasionally -- and against a better team being so aggressive in trying to win the ball back could easily lead to some goals conceded. But the press and high line were the right tools for the job this time out.
The pivot
Without the need for a true holding midfielder (i.e. John Obi Mikel or Oriol Romeu), Roberto di Matteo went with a hyper-aggressive double pivot of Frank Lampard and Ramires. In truth, they each played more like they did in Andre Villas-Boas' 4-3-3 than as deep-lying central midfielders. They were given free reign to go forward as they liked, presumably part of the plan to break down Nordsjaelland with overwhelming force.
It worked. Ramires got a goal and Lampard an assist (he was heavily involved with the third as well, when his pressure on Jores Okore led to a lucky bounce for Juan Mata). Those forward runs weren't necessarily the result of indiscipline -- one would have assumed that di Matteo expected his back four plus Petr Cech to stop anything Nordsjaelland threw at them even without a strong defensive shield -- and they were instrumental in getting the goals.

Figure 5: FCN shot location.
Yes, Chelsea were occasionally caught out at the back, although I thought both midfielders defended reasonably when they were actually around, Lampard in particular. And the Blues did have trouble controlling the game, possibly because the team was stretched so far vertically due to the heavy press being applied at the front (this led to a colossal long ball tally of 54 from Chelsea, of which 42 were successful). But despite that, the hosts offered essentially zero threat (see Fig. 5).
Ashley Cole mopped up the only particularly dangerous cross, and even during the second-half spell where it looked like Nordsjaelland were dominating, the best that they could do was to take some (admittedly very good) shots from range. That does say more about their attacking ability than anything else, but di Matteo put out a plan to beat the opponents in front of him, and it worked.
Flank attacks
Victor Moses clearly deserved a start in a real match. It's not entirely clear that this was one of them. While Juan Mata continued his blistering return to form with a brace, Moses struggled. He was deployed on the left side and repeatedly thwarted by Jores Okore (who was in a thwarting sort of mood), and although he provided the requisite width he didn't actually end up doing much of anything. It was nothing like the dynamic Moses we've seen in substitute appearances.
Why? I'd guess it has to do with the way that Nordsjaelland defended. We've seen 4-3-3 teams turn back fours into threes by advancing the fullbacks and dropping a midfielder into the defence, notably Barcelona, but this time we saw that work with a 4-2-3-1 pivot midfield. Both midfielders often ended up so deep that the Danes sometimes formed a very narrow four-man back line with their fullbacks pushed up on the outside. With such a tight defensive block, quick switches of play to the flanks weren't going to do much good in teasing them out, so Moses wasn't a particularly viable outlet.
Moses' ineffectiveness is at least partially to do with Fernando Torres'. If Chelsea had Didier Drogba (or Radamel Falcao or Peter Crouch or whomever), taking the flanks and crossing would have been a viable option. This year, Arsenal game aside, it's not. Torres isn't beating a physical defence in the air, no matter how clever the delivery.
And this is why Eden Hazard was put on with 25 minutes to go. Hazard doesn't put in the defensive work that Moses does, but he's the man you want to play off Oscar and Juan Mata to help break down a tight defence with his sheer technical skills. The more direct approach cost Chelsea defensively at first, but eventually paid off, with three goals in the final ten minutes (of which two involved clever interchanges down the middle).

Figure 6: FCN shot direction.
Of course, Chelsea weren't the only team attacking down the wings. Bizarrely, Nordsjaelland opted to hit the Chelsea left as hard as they could despite having Branislav Ivanovic isolated on the right. The Victor Moses-Ashley Cole axis held up well enough -- Moses is clearly a fine defensive winger --and despite a full 40 percent of attacks going down the Danes' right flank, most of their shots came from the other side of the pitch (see Fig. 6).
Joshua John was pretty clearly their primary attacking threat. I'm honestly not sure what head coach Kasper Hjulmand was going for here, but it didn't really work. With Juan Mata drifting from an already uncomfortable right wing position, Ivanovic was open to a combined attack from Joshua John and Patrick Mtiliga. By the time Nordsjaelland realised this, it was a bit too late.
Player Influence
Figure 7: Touches from Norsejaelland vs. Chelsea.
Via Whoscored.com, David Luiz and Oscar lead the way in terms of touches (the defender was very good on Tuesday), but then there's a solid block of red. This, of course, is an accurate reflection of the match -- Nordsjaelland had plenty of possession throughout, despite Chelsea's heavy pressing.
But looking at the home side's most influential players (i.e. those with the most touches) tells us that for all of their ball retention, Nordsjaelland had a very hard time involving their forward players in the match. Their positions, in order from most touches to fewest, looks like this: Defensive midfielder, centre back, right back, centre back, left back, defensive midfielder, goalkeeper... and then the attacking players come in. This is a strong contrast to Chelsea, who had an attacking midfielder in Oscar just behind David Luiz.
In fact, let's compare the two sides. Since both played a 4-2-3-1, we'll take the front four as 'attacking players' and the back seven as 'defensive ones' and see what that ends up looking like:
Figure 8: Nordsjaelland touches vs. Chelsea.
Figure 9: Chelsea touches vs. Nordsjaelland.
As you can clearly see, the Blues managed to get their attackers, particularly Mata and Oscar, involved in a way that the hosts simply couldn't match, presumably because keeping their pivot midfielders so deep created a broken team. When you add in the attacking contributions of Frank Lampard and Ramires, it becomes pretty clear that despite not utterly annihilating Nordsjaelland, Chelsea were full value for their win. Remember, the ball did end up in the back of Jesper Hansen's net eight times.
Should they have controlled the play better? Almost certainly. But considering that this was a Champions League away tie (remember Genk), the performance was acceptable. Chelsea did enough to win, if not by the margin shown by the final scoreline.
Jores Okore
It would be remiss of me to wrap up this piece without praising the performance of Jores Okore. He was unlucky on the Chelsea third goal, but his performance is why the Blues didn't end up with a double-digit tally on the scoresheet. That he played so well (four tackles and six interceptions) after having to go off for stitches following a goal-saving collision with Victor Moses early on is extraordinary, especially for a 20-year-old making his second appearance in the Champions League.
On top of his defensive contributions, his passing was very good. He make eight accurate long balls, third most on the pitch, and held a decent 86 percent completion rate on top of that. One game does not make an ace player, but his is a name we'd been hearing about beforehand, and he lived up to his burgeoning reputation against the European Champions on Tuesday night.