Tom Ince fired Derby into the FA Cup fourth round as two quickfire Rams goals stunned West Brom.
The winger grabbed a second-half winner just four minutes after Darren Bent equalised for the visitors to earn a 2-1 victory at The Hawthorns.
In-form Matt Phillips had given Albion the lead but the Rams hit back to beat a side in a higher division in the Cup for the first time since knocking out Sheffield United in 1986.
West Brom lost to Sky Bet Championship Reading last season and the Premier League side repeated the trick against Derby having failed to recover from going behind, with Craig Dawson coming closest to levelling after hitting the post.
West Bromwich Albion 1-2 Derby County
