Chris Boyd hailed Saints' stand-in stars after the 36-13 derby-day demolition of Leicester Tigers.
Boyd was forced to make three late changes before kick-off at Franklin's Gardens as Owen Franks, Courtney Lawes and Dan Biggar withdrew due to injury.
Franks had a thumb injury, Lawes could not shrug off the hamstring problem that had seen him miss last week's win in Italy, while Biggar was struggling with a swollen foot.
It meant Ehren Painter, Api Ratuniyarawa and James Grayson came in to face the Tigers in the Gallagher Premiership battle.
And all three excelled as Saints secured a bonus-point Saturday afternoon success against their local rivals.
"We lost 260 international caps to injury, but Alex Moon came of age in the second row - he was outstanding," Boyd said.
"Ehren Painter continued to make great progress and put in a good effort in the scrum.
"Jimmy Grayson got flogged by the trainers yesterday afternoon then got a call this morning to say Biggs had woken up with a bad foot and he might have to jump in the game, and for him to come in that late and run the ship was a fantastic effort.
"Great credit to our young guys.
"I actually think it was a bonus (to make those changes) because it was a real opportunity for us as a Northampton Saints team missing some really key players so see if we were good enough to do the job.
"The question was about whether we could step up and do the job, and the guys did that today."
Saints scored five tries in all, with New Zealand centre Matt Proctor claiming a double on his Premiership debut.
Api Ratuniyarawa, Tom Collins and Fraser Dingwall also dotted down.
And Boyd added: "We won and got five points, and we played better in more patches than we did badly.
"To get a win for our supporters at home makes it a pretty good day.