Keith Curle has explained his logic behind his substitutions during Saturday's 2-1 defeat to Bradford City.
The Cobblers were leading 1-0 at half-time thanks to Charlie Goode's 21st-minute header, but they dropped deeper and deeper as the second-half wore on, which only invited pressure.
Curle replaced Andy Williams with Vadaine Oliver shortly after the break and also brought on Billy Waters for Matty Warburton prior to Scott Wharton's introduction, in place of Nicky Adams, as Town went to three at the back.
Those substitutions backfired though as Zeli Ismail's fizzed cross was turned in by Clayton Donaldson with 13 minutes to go before Paudie O'Connor's late winner left fans ruing a missed opportunity.
Town supporters were frustrated with their side's negative approach to the second-half, but Curle insisted there was logic behind his various decisions.
"Willo had taken a bit of a knock earlier on and we needed a physical presence up front," he said.
"I thought he did very well in the first-half but we just needed to win that first contact and get us up the pitch, and I've got to say I'm slightly disappointed with Vadaine today.
"I know it's very difficult coming on as a sub but I don't think he held the ball up, I don't think he won enough first contacts and he didn't get us up the pitch enough.
"But that's not all about Vadaine. I thought we lost the connection between midfield and the strikers so he was very isolated."
On withdrawing Adams for Oliver, Curle added: "It was an opportunity to get another header of the ball in the box. The amount of balls they were putting in the box, we needed a physical presence and another contact."