Poly are still very much in the hunt after their victory over Cheltenham earlier in the day.
Penguin will probably look back on the dramatic final stages of the third period as the key to their success.
Manchester had pulled up from 7-5 down to 7-7; and it was 8-8 as Manchester's Kai Dowling netted from distance. Then Penguin's Andrea Tulli produced three decisive minutes of magic.
Firstly, he intercepted a loose Manchester pass to steal possession and swim threequarters of the pitch to score. Just 35 seconds later, he produced an almost identical breakaway goal - and then rounded off the period with a clever long shot from distance into the top right corner.
So Penguin were 11-8 up. Then, at the start of the last quarter, a backhander by centre-forward Mehmet Ali Arat made it 12-8. Victory guaranteed for Penguin? Not a bit of it. Manchester stormed back and were up to 13-12 with 57 very tense seconds remaining thanks to a powerful shot from Dan Paddon.
Penguin held on and can now prepare for a mouth-watering title decider tomorrow (13.45).
Photo (Trevor Hyde): Andrea Tulli scores one of his goals against Manchester today.