A stunning first-half performance saw Swansea bring high-flying West Brom's excellent run to a crashing halt with a 3-1 win at the Liberty Stadium.
Romelu Lukaku pulled one back just before half-time but, despite an improved second-half display, that was as good as it got for Steve Clarke' side.
Swansea struck the woodwork inside 90 seconds. Pablo 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. Nathan Dyer found space down the right and Hernandez steered his deep cross back across goal for Michu to finish from close range - his ninth goal of the season.
The lead doubled less than three minutes later with Hernandez setting 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.
It was 3-0 six minutes before half-time when 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 gave the Baggies a glimmer of hope as he fired home at the end of the first half when Swansea failed to clear Brunt's corner - but that was as good as it got for the visitors.