Tony O’Brien / Reuters
At the Emirates Stadium, Arsene Wenger was again watching from high in the stands as he served his touchline ban and the Arsenal boss was rocked in the 10th minute when former Tottenham defender Younes Kaboul’s powerful strike deflected in off Aaron Ramsey.
Watford suffered an embarrassing FA Cup defeat at third-tier Millwall on Sunday and had gone seven league games without a win.
But the view from the posh seats got even more uncomfortable for Wenger three minutes later as Troy Deeney doubled Watford’s lead with a close-range finish after Etienne Capoue unhinged the Arsenal defence.
Alex Iwobi got one back for Arsenal when the young winger rammed home from Alexis Sanchez’s cross in the 58th minute.
Gunners forward Lucas Perez hit the crossbar in the closing stages, but Watford held on for their first league victory at Arsenal since 1988.
Arsenal is now nine points behind Chelsea in third place.