Fenlon's men responded to his tirade as they came from three goals down to beat the Bairns 4-3 after extra-time to reach a second successive Scottish Cup final.
"It was a horrendous first half, but we showed tremendous character and played really well after that," Fenlon said.
"It wasn't much of a team talk and more of a rant but it worked. But in fairness to the players they knew they'd let themselves down and the fans.
"I felt like leaving myself at half-time. It was difficult to watch and difficult to take and I apologise to the supporters for that first half, and that's down to me.
"But what they have shown is that there's massive, massive character within the group and they've shown that in spades, and that end of the game was different class."
Midfielder Alex Harris inspired the comeback with a goal just after the break and an assist for Leigh Griffiths to cut Falkirk's lead to a goal.
However, the 18-year-old insists the squad will remain grounded ahead fof next month's final against Dundee United or Celtic.
Harris said: "We can't get carried away. The first half was very poor. The second half we turned it around and we had the momentum going into extra-time, but we won't get carried away."