The Dons dominated Friday's FA Cup first-round tie but Zac Barrett was outstanding in goal for the hosts, with Stephen Gleeson and Luke Chadwick both striking the woodwork.
Harford said: "In all fairness to Cambridge City - fair play to them.
"They set out their stall and defended magnificently - you've got to give them a little bit of credit, their goalkeeper especially, and the back four threw themselves in front of everything.
"We created numerous opportunities and we were never in danger of losing the game but you're always wary of a breakaway goal or a set piece.
"The shape of our team is great and we move the ball around very well but we had a game which, in a way, has typified our season where we haven't finished things off."