Whitlock was delighted with his finish under pressure.
"That's probably my best, under pressure, what a fantastic finish! I needed it so badly," the number five seed told Sky Sports.
"When he went 3-2 up in the last set I thought 'I've got to pull something special' and I did."
Chisnall hailed Whitlock's 152 but believed he had contributed to his own defeat.
"I played alright there, but I had too many slack darts," he said. "Simon's a brilliant player. That 152, I can't believe it."
