West Brom 4-2 Cardiff
A Simon Cox hat-trick guided West Bromwich Albion into the FA Cup fourth round as they survived a Cardiff City fightback at The Hawthorns.
Peter Odemwingie opened the scoring after seven minutes despite the home side's strong appeals for offside.
Cox headed in West Brom's second from Nicky Shorey's free-kick before the visitors rallied through Rob Earnshaw and a Joe Mason solo strike.
But Cox sealed victory with a 25-yard shot off the post and a late tap-in.
The Republic of Ireland striker had only scored once this season prior to this match but he quadrupled his tally as injury-hit West Brom enjoyed an FA Cup distraction from their Premier League troubles.
Unusually for a top-flight versus Championship clash, it was the lower league side that made wholesale team changes as the Bluebirds swapped 10 players from Monday's win over play-off rivals Reading.
Cardiff manager Malky Mackay's decision to rotate his squad was due to having one eye on Tuesday's Carling Cup semi-final first leg against Crystal Palace but West Brom counterpart Roy Hodgson had no such luxury.
The Baggies were without seven injured players, including captain Chris Brunt, but they went close to taking the lead as early as the second minute.
James Morrison's effort appeared to strike Cardiff defender Dekel Keinan on the arm but referee Lee Probert dismissed the home side's loud protests.
And the officials were the centre of attention again for Odemwingie's opener as Cardiff argued the Nigerian international was yards offside when he struck on seven minutes.
The Baggies striker showed great composure as he strode on to Craig Dawson's ball before clinically finishing past Cardiff keeper Tom Heaton for his fifth of the season - and the home side's first goal for four hours and 45 minutes.
Hodgson's side cruised into a two-goal lead when Cox glanced in his first of the afternoon from former England left-back Shorey's free-kick on 33 minutes.
Cardiff finally came to life, pulling a goal back through Rob Earnshaw's typical goal-poacher's finish only three minutes later.
The Wales striker, starting his first game for three months as he returned to his former club, found space in West Brom's penalty area to celebrate his 400th career start with a goal as he guided Filip Kiss's cross past goalkeeper Ben Foster.
Heaton made a fine save from Graham Dorrans' shot and Cardiff levelled just after half-time as Earnshaw turned provider for substitute Joe Mason.
The young striker rounded Foster to convert from an acute angle as the Championship side sensed a cup upset.
But West Brom responded, with Shorey hitting the Cardiff crossbar with a 25-yard drive just before Cox took over to secure safe passage through the fourth round for the fifth time in six seasons.
The 24-year-old left Heaton helpless in the Bluebirds goal as his 25-yard effort fired in off the post to give the hosts the edge in this topsy-turvy cup tie.
Heaton kept Cardiff in the game with another fine save from substitute Marc-Antoine Fortune before James Morrison missed an open goal for the Baggies.
The Scotland international jinked around Heaton, but with the goal at his mercy only managed to find the side-netting.
Hodgson, whose side had only won twice at home previously this season, had to rely on Cox to seal West Brom's first win in six games as he converted Odemwingie's drilled cross from close range.