The Quakers fielded six new signings as Steve Staunton's men recorded their first away win of the campaign.
After a drab first half Purcell gave the visitors the lead just after the break as he netted left footed from inside the box, and Gary Smith doubled the advantage just after the hour, sliding the ball home from Mor Diop's defence splitting pass.
Sub Micky Cummins hit back with a left footed volley as Gary Roberts' corner wasn't cleared, but despite a host of chances, the best falling to Ian Sharps who headed over from four yards in the closing seconds, the Millers were deservedly booed off.