Egypt's sixth-seed Momen had to twice come from a game down to win a 77-minute encounter against Swiss national champion Nicolas Müller, who played his best match of recent years to come within a whisker of a huge upset.

Momen lost the first and third games and saw a 7-3 lead in the fifth eroded before winning the marathon encounter 12-14, 11-9, 7-11, 11-8, 11-9.

“There are so many mixed feelings right now - that was two hours of nervous breakdown,” he said.

“I’ve never seen him play that well and he’s improved physically as well.

"Many times I thought he’d feel the work and the effects of the rallies but he just kept fighting back."

Eighth seed Castagnet had to dig similarly deep to recover from 2-0 down to beat in-form Egyptian Ali Farag, winner of the Motor City Open last month.

The Frenchman eventually triumphed 8-11, 7-11, 11-6, 13-11, 11-1 in 71 minutes.

Egyptian third seed Omar Mosaad was also forced over the 70-minute mark in a 11-9, 9-11, 11-4, 11-9 victory over England's former world number one James Willstrop.

There was a better result for Willstrop's compatriot Nick Matthew, with the second seed beating American wildcard Chris Hanson 11-6, 11-5, 11-6 in just 35 minutes.

In the women’s draw Egypt's defending champion Raneem El Welily began her title defence with an emphatic victory over Coline Aumard of France, taking just 20 minutes to see off the challenger for the loss of just six points, 11-3, 11-3, 11-1.

Top ranked American hope Amanda Sobhy put in a similarly emphatic performance in her opening encounter.

She took just 19-minutes to get past yet another Egyptian in Salma Hany Ibrahim, 11-2, 11-4, 11-5.