Rob Holding didn't know he'd be playing against Boro
Holding was called up by Arsene Wenger to play in a back three alongside Gabriel and Laurent Koscielny.
The move took Boro off-guard – they fell to a 2-1 defeat – and the player too.
Holding, 21, said: “I wasn’t sure I was in the team. But with Gabriel and Laurent Koscielny alongside you it’s a lot easier.
“I’ve played in a back three before and you’ve just got to keep working together and communicating.
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Petr Cech – 7: Made a crucial save when the defence failed him
Rob Holding celebrates Arsenal's 2-1 win over Boro
I wasn’t sure I was in the team
Arsenal star Rob Holding
“As long as you keep sliding across as a unit then you’re alright. We’d done it in the week and then we did it in the game.
“Koscielny was the central one, pulling the strings with us both and telling us where to go, so with someone like him and his experience it makes it a lot more comfortable.”
Holding hadn’t featured for the Gunners since February, when he played in the FA Cup against Sutton.
The appearance at the Riverside was just his fourth Premier League start all season.