Armand Gnauduillet's header in the 87th minute and Tendayi Darikwa's strike two minutes into stoppage time snatched the Spireites their fourth League Two win in their opening five games against 10-man Pompey.
He said: "We didn't play well in the second half - we were poor and didn't move the ball quickly enough.
"We were making bad decisions all over the pitch. But to come to a place like this and get a win; we must give the lads great credit.
"It was a fantastic result. It wasn't a fantastic performance, but it was certainly a fantastic result.
"We think we've got goals in our team. Unfortunately, we never looked like scoring. When the big fella (Gnauduillet) came on, fair play to him, it was a great goal.
"It was the first time we had passed the ball well and put quality in the box. We scored a goal and maybe there is a message in that."
- Sports & Recreation
- Tendayi Darikwa