Mark Jones put in a yeoman's effort with the ball, opening up and bowling 14 straight overs to finish with 4-55.
In reply, Saracens started off at a snail's pace, collecting most of their runs from byes and the rarest of singles as they limped to 1-25 off 17 overs.
It appeared Collegiate might pull off the unlikely upset by defending their small total, until the surviving member of Saracen's top order Ben Lewis (39 not out) was joined by No 9 Ollie Gordon (20no) to steer the visitors home.
"I think we lost five for 20 runs at one stage there in the middle," said Rayner. "Then those two came in and it was about 77 [run partnership]."
Collegiate bowlers shared the wickets, with the likes of seamer Oliver Paine picking up a couple.
Results: Porter Hire Premier 1: Wanganui Collegiate 132 (M Jones 4-55) lost to Marton Saracens 133-7 (B Lewis 39no, O Gordon 20no).
Porter Hire Premier 2: Saracens 131 (Kilmeister 27, G Marshall 32, B Morgan 2-9, D Holly 2-27) lost to United 132-6 (A Kenny 81, J Carroll 3-20).
Renegades 230 (A Hodson 59, M Deighton 39, R Slight 30no, A Heap 29, C Friedel 4-39) beat WHS 88 (A Heap 4-25, A Hodson 3-15).