United won 2-1 at The Eyrie against a side from a level above them thanks to two goals from substitute Milo Keane, Tom Coles having earlier given FC the lead just after half-time.
And despite the result, Northfield felt his slightly depleted side did well at times in the game.
He said: “I was quite pleased with it. We changed the whole side in the second-half and there are a lot of new boys that are trying to prove that they’re good enough to sign for the first team and I thought one or two of them did well.
"I was also pleased to see Adam Wedd back as that’s his first game of football for six or seven months.
"We had to play a different shape due to personnel really as we were struggling a bit with attacking players due to holidays and cricket, but we were pleased with the side we had out there.
"In the first 20 minutes United were far more dangerous than us, then in the second 20 we probably started to catch up on a few chances.
"The first ten of the second-half was pleasing and we took one of our opportunities, then made a few changes and it was good to get a lot of the reserve boys in as there were seven or eight on the pitch that won their league last year.
"At the end of the day it’s about minutes – we’re not blessed with loads of fixtures this year and we lost one we’d have liked to have played but have a couple of special ones coming up but in terms of where we are and when we start the season, I think we’re in good order.”
Next up for FC is a home game with Luton Town’s U23 side on Friday night.
United, meanwhile, were back in action on Wednesday night when they ran out 4-3 winners at home to AFC Dunstable thanks to goals from Yemi Adelani, Markel Cousins, Kye Andrews and Taylor Rhiney.
They next go to Letchworth Eagles on Saturday then Kempston Rovers on Wednesday night.
Biggleswade Town, meanwhile, won 2-1 at Raunds Town on Saturday with goals from Joe Howe and Liam Smyth. They will host Stevenage U19s on Saturday before going to St Neots Town on Tuesday night.