A brace from striker Daniel Lomotey and goals from Majeed Ashimeru, Emmanuel Boateng and Bukari Ibrahim handed Hearts their fourth defeat of the campaign.
“We had a very bad day and so many players under performed," Nuttall said.
"Aside that, some of the individual players didn’t follow my instructions.
"It was a bad day in office, very bad one but not the pitch. In spite of the defeat, we have to give credit to where credit is due, Wafa played well against us and deserved to win the game. They were better than us," he added.
Hearts, on the other hand, sit third on the log with 27 points, eight points behind Wafa with 13 matches remaining.