In the first half Everton were probably the better team and we weren't quite our normal selves. We normally have a lot of possession at home and we didn't quite have that and they created a few chances. We found it hard to get a foothold in midfield. Roberto Martinez is a fantastic manager and they had their wide men coming inside and they had numbers in there.
-Frank Lampard. Source: ChelseaFC.com.
We had a very good start, in the first 20 minutes we were in control and had a few good chances and positions to shoot. For the rest of the first half Everton were in control.
They are very comfortable on the ball, pass the ball very well and even though they don't create a lot of chances the quality of their possession is second to nobody in the Premier League... if they scored before us I don't think we're a team who would have been able to score two goals and win the game.
-Jose Mourinho. Source: ChelseaFC.com.
At halftime against Everton, things didn't look great. From the pattern of the game, first twenty minutes aside, it looked like it was the Toffees who were the home team. They were pressing high up the pitch and seemed to be able to slash through the flanks at will. With Chelsea in desperate need of a win to ensure they'd hold onto their place on top of the table, something had to change.
What in particular was the problem? It's all well and good to say that Everton were in control, but Mourinho gets paid to figure out how this came to be. What was going on? Why? Here's my stab at the answer:
Oscar had a poor match. That led to an interesting chain of events. Willian and Eden Hazard had to come into the centre to provide options in the attack and press the Everton pivot of Gareth Barry and James McCarthy; that freed up Leighton Baines and Seamus Coleman to attack because the flanks weren't covered properly. Similarly, the threat provided by the midfield pairing frequently drew Nemanja Matic out of position, allowing Everton's forward three to roam almost at will.
Hazard and Willian coming inside into more congested areas made them less effective and meant that Chelsea didn't have a real threat out wide. Meanwhile, Everton -- who are staggeringly good at attacking fullback play -- were making use of the vacated space and the cascade of positional adjustments we were making to try to hold them off. That led to chances on crosses and on pullbacks. Not particularly dangerous ones, it must be said (Steven Naismith isn't that difficult to shut down), but chances nonetheless.
Simply replacing Oscar with a less injured player was an option, but Mourinho chose to address all of these problems at once by swapping him for compatriot Ramires and switching Chelsea to a 4-3-3. With Ramires' introduction, the Blues matched Everton's shape in the middle of the park. Frank Lampard and Ramires were up against McCarthy and Barry, leaving Matic able to control the area in front of the defence without allowing their midfielders time on the ball.
Lampard and Ramires also solved some of the problems with Chelsea's attack, leaving Hazard and Willian free to stay on the flanks. There they pressed Leighton Baines and Seamus Coleman far more effectively than they did in the first half; the two were non-factors for the rest of the match.
Ultimately, the game was decided late, and it could easily have gone a different way. But second half was a very difficult affair from the first. Everton were toothless, and Chelsea were genuinely in control. Had we played like that all match, we'd have won by more than an injury-time goal; as it was we probably have Mourinho to thank for getting back in the driver's seat.