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GILLINGHAM surrendered their nine-match unbeaten run with a performance that will rank among their worst of the season on Saturday at Deepdale.
Andy Hessenthaler's side,who went into the game looking for a win in preparation for Tuesday's FA Cup replay at Leeds, were always second best to Preston.
They fell behind in the 27th minute when Preston's United States international Eddie Lewis curled the ball wide of goalkeeper Jason Brown.
Graham Alexander increased their lead with a 37th minute penalty after Hessenthaler was penalised.
Gillingham's misery was compounded in the 54th minute when centre-back Barry Ashby put through his own goal.
It was Preston's first win against Gillingham at Deepdale since November, 1996.
Attendance: 12,121.