The Hatters opened the scoring after just eight minutes when James Collins converted from Jack Stacey's cross, after the defender had been picked out on the right by Andrew Shinnie.
Ryan Tafazolli was shown a red card with just over 20 minutes on the clock after a high challenge on Shinnie, and the Hatters punished Steve Evans' side minutes later with a carbon copy of the first goal.
Collins had his hat-trick goal after wonderful work from Kazenga LuaLua and Luke Berry got his first of the campaign with a neat turn on the edge of the box and a calm finish into the bottom corner.
Harford said: "All credit to the players. They have been absolutely different class in terms of how they've trained, how they've gone about things, the way they've acted since we lost our manager. They've been totally and utterly professional and I take my hat off to them. The three games I have been in charge I couldn't be prouder of them, each and every one of them, the ones who haven't been involved have been supportive.
"I would just like to give my thanks to the players for the way they've worked, the way they have gone about their business in the last seven to ten days, it's been a bit of a whirlwind! We're delighted with the performance – obviously the win, the clean sheet, people will say the sending off will have a bearing on it, but I thought we were in total control of it football wise, we were a bit sloppy at times in the first half. But overall a thoroughly good performance."