Arsenal’s 3-1 defeat by Chelsea felt somewhat familiar; it was their seventh loss from their past eight visits to Stamford Bridge. However, whereas Arsène Wenger has frequently been accused of tactical naivety after these defeats and ridiculed for failing to adapt his tactics, on this occasion Arsenal’s manager had attempted to surprise Chelsea with his lineup.

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Having played a 4-2-3-1 system throughout this season, Wenger surprisingly elected to play a 4-3-3. Mesut Özil was moved to the left flank, perhaps to get him into space away from Chelsea’s formidable central midfield pair of N’Golo Kanté and Nemanja Matic, and the versatile Alex Iwobi shifted infield to play alongside Alex Oxlade-Chamberlain, with Francis Coquelin in the holding role. Wenger wanted Arsenal to press Chelsea and in the opening minutes Iwobi and Oxlade-Chamberlain shut down Kanté and Matic effectively, giving Arsenal the upper hand. Wenger’s side enjoyed time on the ball in deep positions and took the game to the league leaders.

Marcos Alonso’s headed opener was somewhat against the run of play but it was a neat demonstration of the problems opponents face against Antonio Conte’s system. While generally depicted as a 3-4-3 shape, Chelsea essentially defend with five players – the three centre-backs and the two holding midfielders – and attack with five players, the wing-backs racing forward to join Chelsea’s three forwards. They often overload the opposition back four.

Facebook Twitter Pinterest Arsenal’s four defenders at Stamford Bridge found themselves overloaded against five Chelsea attackers Photograph: Guardian

For their crucial opener, Chelsea switched the ball out to the right wing-back Victor Moses, who was confronted by Arsenal’s left-back Nacho Monreal. Then Laurent Koscielny tracked Pedro’s run into a wide position and Shkodran Mustafi felt compelled to chase Eden Hazard into the channel. This meant Arsenal’s right-back Héctor Bellerín was isolated against the powerful Diego Costa and while the striker’s initial header from Pedro’s cross hit the crossbar, the ball looped up invitingly for the left wing-back Alonso to nod home. He overpowered Bellerín to such an extent that the right-back was forced to be substituted after an elbow to the face and a heavy landing, with Wenger calling it “100% a foul”. Bellerín was largely blameless for the goal, unable to cope with Alonso’s extra height and a running jump.

However, this underlined Arsenal’s problem – their back four were in effect charged with stopping five Chelsea players in this move: Moses, Pedro, Hazard, Costa, Alonso. Theo Walcott arguably should have tracked Alonso’s run and helped out Bellerín but he was playing on the right of a 4-3-3 in this system. The fact a right-sided forward was blamed for not making a last-ditch headed clearance inside his own six-yard box summarises quite how dramatically Chelsea’s system drags opponents out of shape.

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Arsenal struggled to get themselves back into the contest. Their attacking play was unusually devoid of identity, with Alexis Sánchez starting in the centre-forward position for the first time since mid-December. That was the right option for this game but as Arsenal had become accustomed to the more static, aerially dominant Olivier Giroud playing up front, they had perhaps forgotten how to provide the nippy Sánchez with service. For all the questions about Arsenal’s physicality and mentality, Sánchez and Özil failed to provide their usual moments of magic. Arsenal’s best chances came from headers: Gabriel Paulista and Mustafi were left unmarked from point-blank range, and Giroud nodded home a late consolation. Notably, this means Chelsea’s past four Premier League concessions have been from headers – after a double from Tottenham Hotspur’s Dele Alli and the midweek effort from Georginio Wijnaldum of Liverpool.

With Arsenal 12 points behind Chelsea, their title chances are in effect over and Wenger must start preparing his side for the 15 February trip to the German champions, Bayern Munich, now coached by the former Chelsea manager Carlo Ancelotti. Whereas Bayern’s tactics were gloriously unpredictable under Pep Guardiola, Ancelotti uses a much more consistent 4-2-3-1 system that wily opponents may be capable of outfoxing. Wenger, and Arsenal, must show considerable tactical acumen to progress to the quarter-finals for the first time since 2009-10.