A scuffed shot from Zola then led to Joel Grant doubling Crewe's advantage before the Congolese striker made it three with a header from Ashley Westwood's centre.
"I enjoyed that because we never looked in trouble by half-time," said Gradi.
"We hit the bar twice early on and I thought it was going to be one of those days so I was glad when we went in front. We played well in the first half but to be honest they were pretty bad.
"They played better in the second half and were much harder to beat but they never looked like troubling us. We didn't play as well in the second half, but it was nice to get a clean sheet."