McDonald, Richards and Bull were able to tack on to the back of the group, which had changed as several of the original break riders had been dropped earlier.
Te Awamutu visitor Stephen Collings dragged his co-markers down Warrengate Rd as they caught and passed the third-break riders.
With Forrester, Allan Luff and Vlad Stewart in the mix and a tailwind at their backs, they were always going to be hard to peg back.
Chasing hard was the scratch group Bevan Cheatley, Adrian Pettit and Jason Sturzaker and although they had made up the deficit to break riders earlier on, they had a big job in front of them.
The frontrunners, sensing victory, were fairly motoring in the latter stages.
In the end, the task was too much and the front group of eight were able to stay clear, just.
Approaching the Durie Hill School finish, Forrester called on his experience to power clear of his rivals getting his wheel across the line just ahead of the promising teenager Stewart, who is in the early stages of a comeback to the sport after a break over the last year.
Forrester has been in good form lately and his win capped off some decent late-summer performances.
Palmerston North visitor Graeme Bull showed a surprising turn of pace to nail down third spot and claim B-grade honours.
He just headed off last week's winner Lewis Bunker, who turned in another good effort without being quite able to match his rivals in the sprint.
Collings crossed fifth after completing a huge amount of work on the front of the bunch during the running, with McDonald holding on very well for sixth.
Luff and Richards were the last two of the winning bunch to finish, crossing seventh and eighth respectively.
Thirty-six seconds later, Cheatley stormed home at the front of the chasing bunch, his efforts earning him fastest time (1:06:01) for the day.
His scratch bunch companions Sturzaker (9th) and Pettit (13th) were second and third fastest respectively.
In the C-grade 30km out and back race, Alistair Ross sprinted clear of Michaela Walker for a two-second victory.
There was a further six seconds back to tough veteran Jim Callaghan, with youngster Damian Hussey fourth.
Results
A and B Grade: 1. Darcy Forrester; 2. Vlad Stewart; 3. Graeme Bull (first B-grade rider); Fastest time: Bevan Cheatley (1:06:01).
C Grade: 1. Alistair Ross (fastest time 48.31); 2. Michaela Walker; 3. Jim Callaghan.
Winner of sealed handicap: Damian Hussey.