Pope scored twice and was involved in the other two goals as Vale romped into a four-goal lead against the shell-shocked promotion favourites in the first 28 minutes.
Louis Dodds rolled the ball past Scott Shearer to open the scoring after fine play by Pope and Chris Shuker sent him racing clear. Shuker was again the architect when Pope headed his perfect cross inside Shearer's left-hand post shortly afterwards.
Shearer couldn't prevent Pope adding his side's third either as he looped the ball into the net after collecting Sam Morsy's pass. Pope then picked out the run of Ashley Vincent, who sprinted half the length of the field before cracking in a left-foot shot.
Some of Rotherham's 750 travelling fans were on their way home when Michael O'Connor drove in a close-range shot to reduce the arrears. And the visitors had hope for an improbably comeback when Daniel Nardiello slotted a penalty past Chris Neal after referee Mick Russell had spotted a handball.
But Vale's victory was assured just after the hour-mark when poacher Pope added his third and fourth goals to ruin his former employers' afternoon.