A stunning first-half performance saw Swansea bring high-flying West Brom's excellent run to a crashing halt at the Liberty Stadium.
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The Baggies were simply overrun in the opening 45 minutes, a ninth goal of the season for Michu and a Wayne Routledge double giving their hosts a 3-0 lead.
Romelu Lukaku pulled one back for the Baggies just before half-time but, despite an improved second-half display, that was as good as it got for Steve Clarke' side.
Swansea are on a run of just one defeat in their last nine games and manager Michael Laudrup will have been delighted as his side produced their best display of his reign, with the interchangeable trio of Routledge, Nathan Dyer and Pablo Hernandez ripping the visitors apart.
Albion were looking to record a fifth straight win in the top flight for the first time in 34 years, but their hopes of doing so were effectively over when they trailed 2-0 inside 11 minutes.
They had a warning when Swansea struck the woodwork inside 90 seconds.
Hernandez's exquisite pass played in Michu, but the forward's low shot struck the outside of the near post with Boaz Myhill beaten.
Swansea's crisp, incisive passing was causing the Baggies all sorts of problems, and it came as no surprise when they fell behind in the ninth minute.
Dyer found space down the right and Hernandez steered his deep cross back across goal for Michu to finish from close range.
The lead doubled less than three minutes later with Hernandez again the provider.
The club-record signing set up Routledge who, after a poor first touch, found the net as Jonas Olsson's attempted challenge saw the ball ricochet in off his shin.
Swansea's dominance was such that goalkeeper Gerhard Tremmel was merely a spectator for much of the opening half, and West Brom's malaise was exemplified when Peter Odemwingie managed to miscue a simple five-yard pass to Youssouf Mulumbu and send the ball into touch.
Gareth McAuley blocked sharply from Hernandez after another wonderful flowing Swansea move, and Dyer had a penalty appeal waved away by referee Lee Mason as he went down under pressure from Chris Brunt.
But the hosts did not have to wait too long for their third goal.
Dyer, Hernandez and Ben Davies worked some space down the Swansea left and the full-back's ball across the box came to Routledge, who smashed home.
It could have been even worse for the visitors as Routledge and Hernandez again left the Baggies defence dazzled, but Michu could not reach the latter's far-post cross.
Lukaku did at least give the Baggies a glimmer of hope as he fired home with the last action of the first half when Swansea failed to clear a Brunt corner.
The powerful Belgian could have struck again moments into the second half, but volleyed high over the bar from McAuley's pass.
Albion were finally showing glimmers of the form that had propelled them to third in the table with Claudio Yacob and James Morrison becoming increasingly prominent.
But for all their endeavour it was the hosts who looked more likely to add to their tally.
Michu made the puzzling decision to lay the ball off to Dyer after Angel Rangel's pull-back found him unmarked in the box before the forward headed narrowly wide from Hernandez's clipped centre.
Myhill got down low to save another Michu effort, before Ki Sung-yeung's curling free-kick flew narrowly wide as the Swans claimed a comfortable victory.