Evans' side twice trailed at the Priestfield Stadium but it was the introduction of QPR loanee Hitchcock in the final 20 minutes that proved decisive.
"My substitutions are normally awful but that's the substitution of all time that one," he said.
"He looked particularly bright in the reserves on Monday and there was a thought to start him but the team's been going so well we left him on the bench.
"He's a young man who's going to play at a good level and he's got a fantastic hat-trick.
"We've now got in the play-offs and a lot of managers will be disappointed at their judgement at the start of the season; they made some rubbish predictions because they said we'd fight to stay up.
"Did we deserve to win Yes. By a country mile? Yes, we did.
"We made a couple of defensive errors - Kari Arnason cost us a couple of goals, let's not lie about it. But we're always going to try and win here and if that means putting three strikers on then that's what we'll do."
Source PA