Lamela scored one of the greatest goals in Premier League history with an audacious strike in the first half at the Emirates Stadium. But the Tottenham forward went from hero to villain when he was sent off for a second booking after Jose Mourinho's side blew the lead.
Martin Odegaard had equalised with a deflected effort just before half-time and Alexandre Lacazette sealed the points with a second half penalty.
Lamela's moment of genius was ruined by his red card and it was Arsenal's day as they beat Tottenham for the first time in six games.
Denting Tottenham's bid to qualify for the Champions League via a top four finish in the Premier League was an added bonus for Arsenal, who hadn't defeated their neighbours since 2018.