Grady Diangana inspired West Brom to a third successive Championship win as Hull imploded at The Hawthorns.
The DR Congo international created goals for Matt Phillips and Semi Ajayi to settle the contest for the Baggies in the second half.
The clash of two teams occupying play-off places at the start of play was level at half-time as Hull skipper Lewie Coyle volleyed in an equaliser after Jean Michael Seri's dreadful error had handed Albion's Jed Wallace the opener.
The Baggies stepped up the pace after the break to stay in fifth place in the table and push play-off rivals Hull down to ninth.