Over the course of Chelsea's past 27 matches in all competitions, in which they have been defeated just twice, there has been much debate on how to stop Antonio Conte's juggernaut. Many tactics have been put into practice to differing degrees of success without conclusive solutions being found.
The first theory was mirroring the Blues' formation and deploying a three-man defence in order to directly match up against them. Such thinking was blurred, given that almost every team that tried it was using a system they were unfamiliar with against a team that practiced it regularly. Sunderland, Bournemouth, Stoke, Leicester and Hull all came unstuck in the weeks either side of the New Year, losing 1-0, 3-0, 4-2, 3-0 and 2-0 respectively.
West Brom attempted something entirely different when they came to Stamford Bridge in December. Tony Pulis deployed four natural centre-backs across the defence and two holding midfielders to deny space to Chelsea's attacking quintet of Diego Costa, Eden Hazard, Pedro Rodriguez, Marcos Alonso and Victor Moses. It wasn't designed specifically with Chelsea in mind as Pulis has used it regularly before and since, but it almost worked, with the Blues requiring a late error from Gareth McAuley and ruthless opportunism from Costa to secure a 1-0 win.
Although Chelsea lost 2-1 to West Ham in the EFL Cup in October, Conte had fielded a much-changed side, so the only real occasion when his first-choice team was defeated after starting with three centre-backs was in January's 2-0 reverse to Tottenham. Spurs boss Mauricio Pochettino chose to match Chelsea's formation, with the difference being that his side are used to switching between defensive formations. Not only that, but he specifically targeted a perceived weakness by exploiting Cesar Azpilicueta's relative deficiency against the aerial ball together with Victor Moses' defensive inexperience. It worked well for Tottenham, with two crosses from Christian Eriksen being headed home by Dele Alli to condemn Chelsea to a 2-0 loss.
Formations such as those seeking to batter Eden Hazard have had little success against Chelsea over the last 27 matches.
Suddenly it seemed as if a potentially catastrophic crack in Chelsea's armour had been detected. So when they made the trip across London to face West Ham, it was little surprise to see the titanic Andy Carroll in Slaven Bilic's starting XI and an endless series of crosses fired his way. What West Ham had not legislated for was that Conte had clearly worked on this area in the aftermath of the White Hart Lane defeat. The result was that Carroll barely had a sniff of goal, with both Azpilicueta and Moses emerging victorious from their aerial battles against the best exponent of heading in the Premier League. At the other end, Hazard and Costa sealed a 2-1 win.
Burnley, meanwhile, attempted something even more prosaic: physical intimidation. To be fair to manager Sean Dyche, his team are an extremely well-organised unit and are a credit to his martialling of resources but it cannot be denied that, especially at Turf Moor, they are fond of "leaving one on" their opponents. Ashley Barnes, for one, could regularly be seen leading with his elbow when challenging in the air -- catching Azpilicueta on more than one occasion. Joey Barton, to the surprise of absolutely nobody, was no shrinking violet either. But referee Kevin Friend was happy nothing was untoward and Burnley deservedly earned a 1-1 draw.
Burnley's display that day seemed to be the new template for Chelsea's last two opponents. First, Manchester United embarked on a ritual kicking of Hazard in the FA Cup quarterfinal. Jose Mourinho had singled out the player for rough treatment despite having ironically demanded more protection for the Belgium international during their time together at Stamford Bridge. The ploy failed, with Ander Herrera sent off for twice felling Hazard and N'Golo Kante grabbing the winner in a 1-0 victory for Chelsea.
Undeterred, Stoke then tried a similar rugged approach last Saturday, which in fairness is the same one that they always use when Chelsea come to town. Deliberately trying to goad Costa into lashing out and hacking down Willian, Pedro and Alonso at every opportunity, Mark Hughes' team reverted to type. Phil Bardsley was especially true to form and should have been sent off for plunging his studs into Costa's thigh in the first half well before his eventual injury-time dismissal. The whole display from Stoke was a naked attempt to cow Chelsea into departing the Britannia Stadium defeated, bruised and with their tails between their legs. Instead, Conte's side scrapped away while continuing to play their football before Gary Cahill grabbed a late winner in front of an ecstatic away support.
Conte's men have shown they can cope with the physical battle and an aerial bombardment. They can play on the front foot and on the counter-attack. Sam Allardyce's Crystal Palace will be the next team to try to come up with a way of beating Chelsea. It will be interesting to see the former England manager's solution to an increasingly perplexing conundrum.