Trailing 3-0 shortly after half time the Saints responded with three goals in a six-minute spell to level the scores.
They then pulled away to lead 5-3 before holding out late on as Trinity three times were denied pulling goals back.
St Peter manager Jon Trigg said: ‘No cups of tea were thrown at half time.
We tweaked the system having to commit bodies forward knowing that tactically Trinity would have a dilemma of how they would approach the second half.
‘It was a memorable evening and the players deserve all the praise for a second-half performance that had the mark of a top side written all over it.
‘It was a great comeback, I still can’t quite believe it!’ Trinity striker Stephen McCarter said: ‘We were devastated at the end, we had chances to finish them off but didn’t take them.
‘Once they got their first goal it gave them belief.
After that they didn’t stop running.
They played lots of one-twos and got in behind us.
‘They were also dangerous with Peter Vincenti nodding the ball back inside.
It was disappointing and now we will focus on winning the Jeremie Cup away to North on Saturday week.’ Following an even 35 minutes with chances few and far between the game bust to life with two Trinity goals from Steven McCarter and John Rutter inside a minute.
McCarter added a third after the break, before St Peter hit back with goals from Marco Vieira, Vincenti, Ashley Dodd (own goal), Scott Walsh and Ryan Durand.
Full report in tonight’s JEP.