Arsenal manager Arsene Wenger has criticised referee Martin Atkinson for allowing Chelsea's first goal to stand in his side's 3-1 loss at Stamford Bridge.
Marcos Alonso opened the scoring for the Blues 13 minutes in after reacting quickest to tower over Hector Bellerin and nod the ball in from a rebound.
The Spaniard did appear to lead with his arms as he leapt and caught Bellerin in the face, leaving his compatriot groggy and needing to be replaced by Gabriel Paulista following some on-field treatment.
Wenger says that he did not have to think twice before bringing off the full-back, but believes that the officials should have spotted the infringement in the build-up to the key opener.
"The decision [to take him off] was very quick," he told reporters. "You have to respect it's the head. One of the particularities of the game today is that referees are much more severe with tackles on the ground and let more go with elbows in the face.
"It is not only today. In many games I see that but it is more dangerous to hit the head. But we are maybe not good enough in possession to make our game more dangerous.
"We lost goals in positions where you cannot afford to lose it. It leaves us to focus and prepare on the next game. It is very difficult to come out individually on players. We were not at our best in some positions."
Eden Hazard and former Gunner Cesc Fabregas went on to put Chelsea three goals ahead, before Olivier Giroud pulled one back for the visitors in added time.
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