Hartlepool substitutes David Foley and Richie Barker compounded West Brom's miserable start to the season by dumping the Barclays Premier League side out of the Carling Cup.
Robert Koren's 87th-minute strike had denied the League One outfit victory in normal time after Joel Porter had fired them into a 61st-minute lead.
But Foley and Barker scored within three minutes of each other at the end of the first period of extra-time to make the score 3-1, with the Baggies hitting the crossbar on three occasions.