Albion lead their arch rivals Crystal Palace 3-0 at the break after an incident-packed first half.
Albion won a penalty after Jose Izquierdo was clattered into – and Glenn Murray converted the spot kick
Minutes later Murray was upended by Wilfred Zaha but referee Kevin Friend only gave a corner.
Then Shane Duffy was sent off for an off-the-ball incident.
From the resulting corner substitute Leon Balogun, with his first touch, put Albion 2-0 up.
Palace offered little then in the final minute of first-half stoppage time Florin Andone – on as a sub for Murray – chased a lost cause and, despite two defenders in attendance, put Albion into an unbelievable 3-0 half-time lead.