And five minutes later, it was Sanchez with the cross and it was met with a clinical header by Ozil.
In a bid to get back into the game, Watford boss Walter Mazzarri made a change at the break bringing Pereyra’s on for his debut in place of Guedioura.
And the Argentine signed from Juventus gave his side hope after the ball landed at his feet in the box and he finished well past Petr Cech.
For the next ten minutes, Arsenal came under the cosh and Cech rescued his team with a double save to keep out Holebas and then Ighalo.
But the away side held on to get a vital three points ahead before the international break.