Without a win in five, the Bantams went into their game at Sixfields on a downward spiral in League One and a poor first half saw them punished by Alex Revell's header.
But second-half goals from Mark Marshall and Jordy Hiwula saw City to three points and McCall admitted a change of approach was important.
McCall said: "We went with a diamond (formation) in the first half and for all the control we had, we just didn't put their goal under enough pressure and we had no cutting edge at all.
"I agreed completely with the supporters ironically cheering when we had a shot because we had lots of opportunities to get shots off but we messed about and tried to play through too much.
"In the second half we made it basic and I always knew that the subs in Marshall and (James) Hanson would give us that little edge in the second half and that showed.
"The second half was outstanding, not just the football but the desire and commitment to each other.
"We huffed and puffed and Northampton are a strong unit but I genuinely thought it was coming for us because the fans were behind us and the players were just wanting to attack at every opportunity.
"We said at half-time that we owed the supporters something and a big performance and we got that from each and every one of them, so naturally I'm pleased and it's nice to win a game again."