Arsène Wenger has said using a three-man defence is "not a long-term plan" but believes his tactical change worked well against Middlesbrough.
The manager selected three centre halves for the first time since his very first season in charge – back in 1997 – although he is unsure whether he will stick with the system for the weekend's FA Cup semi-final at Wembley.
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"I don't know, I just felt that sometimes the team needs to believe in something new, something different, just to find a bit of confidence back," the boss told Arsenal Player after the 2-1 win.
"Overall I felt that it worked quite well today because we won the game.
"We had practiced on it before at some stage, (but) we like offensive football so this was a bit more defensive-minded for us.
"I feel overall it is not a long-term plan, but punctually it can work."