Chelsea's 4-2 win against Swansea was made all the more impressive by the fact that the Blues did basically nothing right for most of the first quarter of the game, but came back to demolish their visitors regardless. We've already seen Jose Mourinho blame an incoherent pressing game for the early struggles and showed what he meant and why that's so dangerous for a team. Now let's take a look at how it was fixed.
Defining the problem
Mourinho claimed after the match that the team's pressing references were off in the first half. In tactics jargon, a 'pressing reference' is more commonly a 'pressing trigger', and they tend to be specific opposition tells that indicate the ball is up for grabs -- a pass towards goal, a poor touch, etc. But the most important trigger of all is field position.
All teams set a line on the field beyond which they try to win the ball. This line changes situationally, but it's a fundamental part of defensive tactics. Here, we let them play. There, we don't. Even a team that doesn't press at all in midfield will eventually be forced to step up and engage as the opposition moves into the final third of the pitch. Where a side sets its pressing line is a major part of how they play without the ball.
For the first part of the first half, it appeared as though Chelsea's players weren't all using the same line. While the central four of Diego Costa, Oscar, Cesc Fabregas and Nemanja Matic were attacking Swansea as soon as they moved to the middle third, the wide players were engaging far deeper, allowing the visitors to cross the halfway line before pressing.
Here, for instance, is Oscar chasing down the ball very high up the pitch:
And here is Eden Hazard vaguely waving a leg at his man inside his own half:
Instead of a sensible pressing line, we had something that looked more like a crescent. The centre was sucked out, the ball worked to the flanks, and Swansea -- especially Jonjo Shelvey -- then attacked the vacant space. This happened repeatedly and was the primary reason we looked so completely incompetent. To make matters worse, chasing the ball all over the pitch made us vulnerable whenever, by some miracle, we got it back, which in turn gave a boost to Swansea's already-impressive pressing game.
Mourinho had two problems to solve: make sure the location of pressing line was understood by all of his players (especially the wingers), and find a way to prevent Shelvey's runs into the midfield space that kept getting left open. The second is a trickier issue, more difficult to address on the fly, but the first was dealt with around the 20 minute mark.
Fixing the wingers
Mourinho fixed the first problem in fairly straightforward fashion -- after a quarter of an hour, he yelled at Eden Hazard. Hazard, who'd been extremely passive on the left side, eventually began participating in the press with Oscar. Andre Schürrle, meanwhile, had a slightly more different issue. The German was pressing along the line splitting Chelsea's third from the midfield, not Swansea's, and although he'd identified that there was a problem defensively his response was to come infield to support Matic, which left the right flank open for Neil Taylor to attack.
After the chat with Hazard, instructions to conduct a higher press were eventually communicated to Schürrle, and he wound up working a good 40 yards higher up the pitch than he had been. He still wasn't doing a particular spectacular job on the ball, but at least his off-ball work was coordinated with the rest of the team.
This tweak meant that when Oscar and Diego Costa put pressure on the ball in the middle there was no longer an easy outlet to the flanks. Swansea are a good team, but the reason they have a reputation for possession is because they're happy to keep the ball in their own half, not because they possess technically brilliant players. A coherent Chelsea press quickly disrupted their careful buildup play, and from the time the wingers were pushed up until Diego Costa's first goal the Blues were in control of the match.
But there was still a problem in central midfield thanks to Shelvey's running into the space vacated by the press. A solution to that problem had to wait for halftime.
Ramires and the 4-3-3
Swansea's midfield was set as a 2-1 triangle, with Ki Sueng-Yung static at the base, Gylfi Sigurdsson in the hole and Jonjo Shelvey starting deep then breaking into space. Chelsea were in a similar shape, with Nemanja Matic for Ki, Oscar for Sigurdsson and Fabregas for Shelvey. But they were more aggressive than the visitors, which meant that Fabregas had a habit of chasing the ball up the pitch, opening a hole which Shelvey was only too happy to occupy. This was Swansea's primary means of attacking through the centre, and it threw Chelsea into disarray.
Gary Neville talks at length about the problems this was causing here, and while I don't agree 100 percent with his conclusions -- while Fabregas contributed to the midfield chaos, he wasn't the whole cause -- the clips are definitely worth watching.
After Mourinho sorted out the pressing line by giving the wingers a piece of his mind, he took advantage of halftime to solve the second problem, which was controlling Shelvey's runs into the space behind Fabregas. He did this by inverting Chelsea's midfield shape and introducing Ramires to the mix. André Schürrle was the man sacrificed, with Oscar shunted out to the wings.
In the second half, Ramires was assigned to track Shelvey (at points it looked close to man-marking), Fabregas was left free to press Ki and Matic stayed far closer to home, dealing with Sigurdsson. Although Swansea had a centre back free and speed down the wings, most of the lines of supply they were using in the first half were now comprehensively cut. The fullbacks couldn't move the ball up, the central midfielders were permanently occupied and Chelsea, barring a pair of essentially random breakaways, completely dominated the match. Problems solved*!
*Apart from on the second goal, but I'll let Ramires get away with that one at 4-1 up.