The world number 12 came through 11-7, 11-9, 10-12, 12-10 at Grand Central Terminal, becoming the first Welsh player to reach the quarter-finals of the event since 2002.

Willstrop lifted this title in 2010, but Makin won the all-unseeded duel to continue a superb run at the tournament.

He defeated Peru's seventh seed Diego Elias over five games in round two and can now look forward to a last-eight tussle with Egypt's two-time winner Mohamed ElShorbagy.

"It's obvious to try and go fast and upset the rhythm of James because you get too worried about exchanging up and down the walls with him," Makin said.

"But I think if you try to move the ball too quickly then he's far too good for that. 

"I know I had to really try and straighten up across the back-end and try to play squash how I wanted to and take the middle away from him.

"It's massive [to be in the quarter finals], the win against Diego was huge for me and I knew that was going to be hard today. 

"James has been in great form, he beat [Karim Abdel] Gawad in the last tournament and was coming into this fresh, so I was well aware that it was going to be tough, even though I'm higher than him ranking-wise. 

"I take that as a really good win."

Second seed ElShorbagy, the 2017 world champion, enjoyed comfortable progress against France's Gregoire Marche, 11-1, 11-9, 11-9.

Gawad, the third seed and 2016 world champion, had to come from behind to beat England's Declan James 6-11, 11-5, 11-1, 11-3.

German sixth seed Simon Rösner knocked out India's Saurav Ghosal 11-8, 11-2, 11-9.

In the women's third round, top seed and 2017 world champion Raneem El Welily of Egypt breezed past Hong Kong's Annie Au, 11-9, 11-6, 11-5.

El Welily won the event in 2017 and will now play 2015 champion Camille Serme of France in the quarter-finals.

Fifth seed Serme beat Egypt's Yathreb Adel today, 11-7, 13-11, 6-11, 11-9.

"Just like Annie, Camille and me go way back and have had many matches together," El Welily said.

"Most of them were very close, she is playing very good squash and having to play her in the quarters shows just how good the depth of the game is for the women. 

"It will be a tough match, but hopefully I will be up for the challenge."

Egypt's third seed Nouran Gohar went through by beating compatriot Hania El Hammamy, 11-7, 11-9, 11-6.

England's Alison Waters, seeded 13th, also beat a team mate as she accounted for Emily Whitlock 11-7, 11-5, 11-7.

Whitlock had shocked American home favourite Amanda Sobhy, the seventh seed, in the previous round.