Youssef Ibrahim came from behind to knock top seed Mohamed ElShorbagy out of the Professional Squash Association (PSA) Qatar Classic in Doha and record the biggest win of his career.
The 21-year-old survived a match ball in game four to take the contest to a decider, which he duly won.
Ibrahim's 11-9, 6-11, 3-11, 15-13, 11-6 win over his fellow Egyptian ensures that ElShorbagy - the 2017 world champion - will not return to world number one this week.
"I don’t know how to describe how I’m feeling right now," the world number 41 said post-match.
"I’ve been waiting for a break for a really long time and training really hard for so many years and I haven’t had a good win - this just makes it so much better."
Next up for Ibrahim in the quarter-finals is compatriot Fares Dessouky, the only other unseeded player left in the competition.
Dessouky made quick work of Spaniard Borja Golán, winning 11-2, 12-10, 11-2.
Defending champion Ali Farag is also into the quarter-finals - one of five Egyptian players in the last eight.
The world number one swept aside Eain Yow Ng of Malaysia, an Asian Games team gold medallist, 11-5, 11-7, 11-7.
Farag is seeded second at the PSA World Tour Platinum tournament, and fifth seed Diego Elías will be his next opponent.
The Peruvian beat Colombian Miguel Rodriguez 11-5, 13-11, 11-9.
New Zealand's Paul Coll produced a spirited comeback to book his place in the last eight.
The fourth seed twice trailed France's Grégoire Marche, but was ultimately a 7-11, 11-9, 9-11, 11-6, 11-5 victor.
Egypt's Marwan ElShorbagy, who beat German Raphael Kandra 11-4, 11-5, 11-7, will face Coll for a place in the semi-finals.
Third seed Tarek Momen is the fifth Egyptian into the quarter-finals, following an 11-8, 11-3, 3-11, 11-4 win over England's Commonwealth Games champion James Willstrop.
Welshman Joel Makin - who beat Lacas Serme of France 11-7, 11-9, 11-7 - will be his last-eight opponent.
The quarter-finals are due to be played tomorrow in Qatar.