Rotherham's hopes of an automatic promotion place were severely dented by a 2-1 defeat against Port Vale.
The Millers' best chance of a poor first half fell to Craig McAllister, who needed an extra touch to control Adam Le Fondre's pass and lost the opportunity.
At the other end Sean Rigg forced a good save from Andy Warrington with a fierce drive.
But two goals in as many minutes by the visitors turned the game on its head. A 59th-minute corner was cleared by Rotherham but the ball came in again from Louis Dodds, Pablo Mills missed his clearance and Craig Davies was left with the simplest of close-range tap-ins.
Two minutes later Tommy Fraser's free-kick on the left picked out Marc Richards at the far post and he volleyed past Warrington.
Walker gave Rotherham hope 10 minutes from time with a 20-yard free-kick but the hosts could not find a leveller.
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