Cardiff's seven match unbeaten run ended with defeat at The Hawthorns.
West Brom almost shot themselves in the foot as they powered to the top of the Championship table.
Albion went into a three nil lead and were cruising to victory before sub Danny Ward scored twice in eleven second half minutes to make the hosts think again. City though couldn't find an equaliser and Albion added respect to the scoreline in injury time.
Matheus Pereira (19), Grady Diangana (42), Charlie Austin (71) and Romaine Sawyers (90+3) scored the goals for West Brom with Ward's double (75, 86) in reply for the Bluebirds.
Before Austin's goal Robert Glatzel missed with a header and then had a goal disallowed for offside.
Cardiff can look at Albion and see the level they need to raise their game to if they are to compete at the top of this table. Cardiff have strengths of their own but not the quality that West Brom have as a side who are one of the very real favourites for automatic promotion.
There's a two week gap now before Cardiff kick off the next round of matches with a televised home game v Sheffield Wednesday on October 18th, ko 7:45pm.
West Brom: Johnstone; Furlong, Ajayi, Bartley, Ferguson; Livermore, Sawyers; Phillips (Krovonic 73), Pereira, Diangana (Edwards 53); Austin (Zohore 80)
Subs: Bond, Gibbs, Robson-Kanu, O’Shea
Cardiff City: Smithies; Peltier, Morrison, Flint, Bennett; Pack, Bacuna; Whyte (Murphy 80), Paterson (Mendez-Laing 58), Hoilett; Glatzel (Ward 73)
Subs: Etheridge, Murphy, Nelson, Tomlin, Coxe
Referee: John Brooks
Attendance: 25,140 (1,985)