Robbie Fowler started the rout on 4 mins with a left footed shot past Dean Kiely, Jimmy Floyd Hasselbaink was shown too much respect on 23 mins and he was able to fire home from outside the box.
Just 4 mins later and Joe Ledley was brought down in the box. Fowler scored with ease, sending the keeper the wrong way.
Before the dust had settled City were in the Albion box again and Trevor Sinclair was on hand to make it 4 - 0.
At this stage many home fans were heading through the exit doors.
Albion came back with a goal before half time and a late penalty but the devastating opening 30 mins from Cardiff City made it an almost impossible task.
That was Cardiff City's first win at West Brom in over 50 years. Gerry Hitchens and Colin Baker scored for City in a 2 - 1 win in February 1957. Four goals at The Hawthorns by a Cardiff side equals our best ever effort there, that was in 1923 when Len Davies scored all four in a 4 - 2 win. Davies was in the FA Cup winning side 4 years later.
The draw for round 4 is on Saturday lunchtime around 12:15pm on Sky Sports News.