The Gunners will have been fearing the worst when the Spanish side went in at the break 2-0 up and with the wind in their sails.
Mikel Arteta watched on as things went from bad to worse as Dani Ceballos was given his marching orders.
It was all falling into place for Unai Emery, who no doubt was keen to get one over on his former employers.
But Nicolas Pepe's second-half penalty means it is all to play for in north London next week as Villarreal too finished with ten men after an action-packed second 45.
Full-time
Villarreal 2-1 Arsenal
