Willstrop overcame the world number four, who won the world title in 2016, 11-8, 4-11, 11-9, 12-10 to progress to the last eight at the Khalifa International Tennis and Squash Complex.

He will play fifth seed Simon Rösner for a place in the semi-finals after the German beat Joel Makin of Wales 11-8, 11-8, 11-5.

"I am absolutely thrilled," Willstrop said. 

"It is hard to say because I am on a rush of adrenaline, particularly in these conditions where it is shootout squash. 

"The intensity is cranked up and you haven’t got any time to settle."

Willstrop added: "To be here [the quarter finals], and with a rest day, that is quite positive. 

"It is a fabulous prospect, and hopefully I can get recovered well and do it justice on Wednesday."

Second seed Tarek Momen survived a scare in his third-round match as he needed five games to get past Abdulla Mohd Al Tamimi, the first Qatari player to reach the last 16 at the World Championship.

Momen was 2-1 down before he won the last two games to record a tense 11-5, 10-12, 9-11, 11-9, 11-4 triumph.

The Egyptian's opponent in the quarter-finals will be sixth seed Diego Elias of Peru, who defeated Momen's team mate Fares Dessouky 10-12, 11-8, 11-6, 11-4.

The tournament continues tomorrow.