The big centre-forward opened his account for the Spireites to make it three games unbeaten.
The second half of the the BT Sport game came alive after Matty Kosylo’s composure put the hosts ahead with 20 minutes to go.
Denton put a dent in his old club’s plans and Allen was open about the situation after.
“He almost wasn’t on the pitch,” the manager said following the 1-1 draw.
“I wanted to bring (Marc-Antoine) Fortune on, I knew he would put himself about a bit.
“But we held back for another minute or two and he I am glad we did! It was a fantastic header, he deserved that.
“People need to remember he came here after being a plasterer for five days a week. It wasn’t going to happen for Tom overnight - he has come to a big club and there’s pressure on him but he is starting to show what a good, good player he is.”
Denton said: “I’ve got my first goal - finally!
“It was a great cross and I have put one past my good mate Sam Johnson. I was really pleased with it.
“It’s the first time I have ever been back to an old club. They have good fans here and I have a lot of friends at Halifax but I can’t deny it was good to get off the mark for Chesterfield.”