Former Tottenham defender Younes Kaboul lashed in the opener within 10 minutes for Watford with a shot from outside the area which deflected off Aaron Ramsey.
Just two minutes and 57 seconds later, the visitors doubled their lead as Troy Deeney tapped in after Etienne Capoue’s fine run ended with his shot being saved by Petr Cech.
The Arsenal goalkeeper was called into action again as he tipped Sebastian Prodl’s header over the crossbar and pushed away Daryl Janmaat’s curling strike.
The hosts improved significantly in the second half and Alex Iwobi pulled a goal back by steering Alexis Sanchez’s cross home.
Lucas Perez struck the crossbar with a powerful drive, but they could not find the equaliser.
Who was your man of match?