It was a see-saw contest up front as Feilding looked to monster Metro's props in Keightley Watson and Emanuel Savage.
Grinding away for long periods on attack, they scored two tries – the latter a quick tap on a penalty that was fired out to the wing.
However, Cosford and co-coach Russell Gedye backed their side to weather the storm and run the Yellows out of gas, and so it proved with 29 unanswered points in the second half to the delight of a good crowd.
The forwards brought parity back with a couple of tighthead scrum wins against their tiring opposition, and Metro's speedy backline did the rest.
"You've just got to prove you'll be ready for all occasions," said Cosford.
"First half, it was all over the place – helter skelter.
"I was hoping our fitness would come through at the end and it did.
"We just stepped up another notch and kept it going."
Former Heartland Hurricane Under 20s representative Jack O'Leary scored a hat-trick and popped over a couple of conversions, while Paiki Ponga was back in his preferred position of fullback and also dotted down.
Now with an eight-point gap on the Yellows at the top of the table, Metro will look to cement their spot over the rest of the second round - starting at home this Saturday against Feilding Old Boys Oroua.
However, FOBO (4-3) put a stern test to Metro before losing 27-10 in April and, after just getting by Dannevirke SC 28-25 on Saturday, are in a desperate fight to hang onto fourth place from Freyberg Old Boys (2-2-3).
"Every team's capable [of beating us] on the day, every game's going to be like a final," said Cosford.
"I told the boys, 'win every game from here and you win the championship, stumble somewhere, you may not'."
With no Tasman Tanning Premier or Senior games this Saturday, Metro hope another good crowd will come to watch them play at 12.45pm.
