Arsenal travelled to Watford this evening looking to secure the three points which would catapult them back into the top four.
And they were given an unexpected helping hand by Watford stopper Foster after less than 10 minutes as Aubameyang got on the scoresheet.
Foster dwelled on a back pass from Kiko Femenia, allowing the ball to run across his body after taking a touch so it was on his favoured left foot.
And he paid the price when the alert Aubameyang came steaming in and diverted the ball into the empty Watford net just as Foster tried to boot it clear.
Aubameyang wheeled off in glee having been afforded such an incredible opportunity to get Arsenal going at Vicarage Road.
While Foster was left to dwell on the embarrassing moment which ensured he once again failed to keep a clean sheet against the Gunners.
The unbelievable scenes continued minutes later when Watford skipper Troy Deeney experienced a split-second of madness.
Deeney was sent off for a coming together with Lucas Torreira, in which he appeared to strike the Arsenal midfielder in the face with a flailing elbow.
Sky Sports co-commentator Alan Smith branded Deeney “silly” following the incident, which further damaged Watford’s chances of securing a surprise win.
“Well he’s so much bigger than Torreira, sometimes you just try and arm off your opponent and you catch them in the face accidentally,” Smith said.
“But if it was a deliberate elbow that’s a different matter entirely.
:It’s a little swipe of the arm, something he did not need to do.
“Just letting his man know he’s there but it’s a silly challenge.
“Craig Pawson had a little chat with the linesman who might have helped him.”