Graham Potter’s nine-game Chelsea winning run poetically came to an end against former club Brighton and it was his tactics that were to blame for a 4-1 thumping on the south coast.
The Blues lined up in the same 3-5-2 shape that had helped them win away at RB Salzburg in the Champions League in midweek.
Chelsea were evidently happy with how it worked in Austria, where they ran out 2-1 winners, but here they found themselves 3-0 down against Roberto De Zerbi’s side by half-time.
The Italian coach who replaced Potter had learned lessons from how the youthful Austrian champions got at Chelsea. Junior Adamu’s goal for Salzburg showed that space could be exploited behind Raheem Sterling and, to a lesser extent Christian Pulisic - starting his second game in a row for the first time this season.
The two makeshift wing-backs play a hybrid role that sees them act as high-and-wide wingers with the ball and as defenders off of it. Their inability to track back quickly in transition leaves space on the flanks for teams to attack into.
Sterling had been productive in the final third in the first half but that obvious space in behind was exploited time and again as Marc Cucurella returned to face his former club.
Booed with every touch, Cucurella was the victim of the tactical weakness that was exploited at will by De Zerbi - who had done his homework. It was a nightmare return for Brighton's reigning Player of the Season.
Thiago Silva also struggled physically against one of the league’s best pressers, giving away the ball early on and having to clear the resulant shot off the line. He did so again before the pressure told as Leandro Trossard rounded Kepa Arrizabalaga after the 38-year-old again gave the ball away.
Ruben Loftus-Cheek’s own goal minutes later was an unforced error but Trevoh Chalobah’s at the end of the first half was due to terrible defending down the flanks that gave Pervis Estupinian a chance to exploit the space behind Pulisic.
The next two big tactical decisions from Potter rectified the mess at half-time, switching to a back four with Kepa going off injured in a like-for-like change with Edouard Mendy. Loftus-Cheek played well at right-back and was involved in creating Havertz’s goal early in the second half.
Chelsea regained control of the game but it was too late with Sterling and Cucurella coming off in the 60th minute - an admission of poor performance and Potter’s starting line up error.
Pascal Gross' late fourth goal was a consequence of Chelsea chasing the game and throwing on three strikers in a gung-ho approach, compounding their misery.
Brighton have now given the rest of the Premier League a blueprint for how to face Potter’s favoured system.
Of course, a huge reason for Potter's imperfect tactical choices have been Reece James' injury but the loss of one player should not impact a team so much.
The good thing for Chelsea is that the Blues boss is the master of shifting his shape and he may realise the need for a new plan A that can actually control matches.
If not, they rely on attacking dog fights for points ahead of the six-week break for the World Cup with matches against Arsenal, Manchester City and Newcastle to come.
