A strong south-westerly tailwind for the outward leg ensured the pace was on from the outset.
Chasing them, the 11-strong scratch bunch included Brent Bismark, Adrian Pettit, Bevan Cheatley and club champion Jason Sturzaker.
Also there were Pat Johnstone, Steve Cowan and youngsters Boaz Darby and Lewis Bunker who all worked hard to reduce the deficit to those ahead.
Sean Tucker and Darcy Forrester, both feeling the effects of heavy training loads, were dropped before halfway and while Tucker eventually sought the sanctuary of the sag-wagon, Forrester elected to battle on to the finish.
At the Mangamahu turnaround the front group was still largely intact, but had retained only three minutes of their original 14-minute lead.
Setting off into the stiff headwind, it seemed likely they would be reeled in before the day's major challenge the ascent of Reid's Hill at the 70km mark of the return.
Scrimshaw and company were having none of that though, and with a couple more riders starting to take turns they kept the gap coming to the foot of the climb.
By the steepest part of the ascent Scrimshaw and Groves the latter on the comeback trail after a race crash a month ago slipped away from their companions. At the top they were uncertain about waiting for reinforcements, but heeding the shouted advice of Ron Cheatley, who was following the race, they decided to press on together into the wind.
The core of the bunch re-grouped and settled down to chase the duo, but they were making heavy weather of it.
Similarly further back, the scratch bunch split up on the climb and by the top only Bismark, Bevan Cheatley, Darby and Pettit and Johnstone were left together. Unfortunately Johnstone was forced out soon after by a puncture, a loss that cost the chasers dearly.
It took them until the 81km mark to catch the stragglers from the front group, but they still needed to run down Groves and Scrimshaw.
Up front, with a sniff of victory, the leading pair were giving it full gas with Scrimshaw looking the stronger of the two.
Despite the rapidly closing gap they held on defiantly as Scrimshaw mustered a final sprint to take a well-earned win by a narrow margin from Groves.
A mere 21 seconds later Bevan Cheatley hit the line in third, taking the day's fastest time (2 hours, 19.59 minutes).
Wright put in a great performance to claim fourth and McNeil, improving all the time, did well for fifth.
Bismark was the next scratch rider home after Cheatley.
A bit further back in the field there were some good efforts from John Black, Marty Hewson and Clint Black all part of Cheatley's finishing group.
Veteran Laurence Sunde also put in a terrific ride, hanging tough and finishing not far behind his much younger rivals.
Eight B-grade riders raced the 55km out to Wyllie's bridge past Kaungaroa and return.
It was the Palmerston North visitor Graeme Bull who burned off his Wanganui rivals.
Bull, and locals Craig Bright and Murray MacDonald, slipped away from their companions on the Reid's Hill climb and approaching the finish it was the strongly built visitor who outsprinted Bright to take the win, with MacDonald only a split-second behind in third.
Alan Luff, having an easy race before contesting Sunday's annual Feilding to Apiti event, was fourth.
After a gap, the second Palmerston North rider Noel Macdonald finished fifth from Carl Rusden, Curt Weir and Mark Stoneman respectively.
In the 33km out-and-back C-grade race, the winning trio from last week again filled the top three placings, albeit in different order.
Dean Blackwell returned to winning form, outsprinting Debbie Cain, with last week's victor and promising junior Joseph Loveridge-Mills up close in third. The front three were clear of Julie Weir and Paul Darby, who finished together in fourth and fifth.
Results
A-Grade: 1. Brian Scrimshaw; 2. Phil Groves; 3. Bevan Cheatley (fastest time; 2:19.59).
B-Grade: 1. Graeme Bull (fastest time 1:38.02); 2. Craig Bright; 3. Murray MacDonald.
C-Grade: 1. Dean Blackwell (fastest time 1:00.14); 2. Debbie Cain; 3. Joseph Loveridge-Mills.