Whanganui Metro retained just five players from last year's championship winning team who beat College Old Boys 33-0 in Palmerston North.
As well as gaining plenty of new young players for this 2019 season, coaches Cosford and Russell Gedye are also new to the fold.
Cosford praised his players returning from injury Mason Johnson and man of the match Louis Devine.
"They went really well and the young guys are coming along. They're all lifting to the level we're aiming to be at.
"We know where we've got to be and it's up to us to improve mentally to get there."
The loss left Whanganui Metro fifth on the competition ladder, one point out of the top four on 16 heading into the final match of round one.
They will take on second-to-last placed Massey Ag XV at Massey University in Palmerston North on Saturday, kicking off at 12.45pm.
"[The Massey Univeristy Rugby Football Club] have got their 90th anniversary so it's going to be a hard game and they'll have everyone on deck," Cosford said.
"Our breakdown got dominated by Feilding on the weekend, we've got to start dominating the breakdown if we want to beat them."