In the previous seven meetings between the brothers Marwan had failed take more than a solitary game from his older brother but he managed to come through a compelling five-game battle 1-11, 11-8, 13-11, 5-11, 11-8 to reach the last four today.

It was Mohamed who started stronger, taking the first game 11-1 as he set a blistering pace at the University Club of Chicago.

But Marwan responded to go 2-1 ahead before Mohamed levelled to take it to a decisive fifth game. 

Marwan then sealed his place in the semi-finals by taking the fifth game 11-8, causing an outpouring of emotion from both.

"It's tough - we both knew it was going to happen at some point," said Marwan.

"Every time we play it's a battle on court - but we are best friends off court.

"I'm grateful for the sport - it has allowed me to have my brother as my best friend.

"It's a tough day today for us.

"But I have a big match tomorrow to look forward to and a chance to reach a first World Series Final."

Another Egyptian, world champion Karim Abdel Gawad, suffered a shock defeat to 34-year-old Borja Golan of Spain.

Gawad arrived in Chicago bidding to win a third straight PSA World Series title but found himself up against an inspired Golan, who will now compete in a major semi-final for the first time since the 2014 Hong Kong Open after winning 8-11, 11-4, 11-9, 11-9.

Prior to the tournament the Spanish former world number five had not won a match for six months following a herniated disc injury but produced a tactically superb display to seal the match after 73 minutes.

In the women's draw an Egyptian finalist is guaranteed after the trio of Nour El Sherbini, Raneem El Welily and Nouran Gohar came through to join Frenchwoman Camille Serme in the last four.

After stuttering early in the tournament Gohar secured an eye-catching 3-0 win over England's Laura Massaro courtesy of a dominant performance that saw her control proceedings from start to finish to claim a 11-7, 11-3, 11-5 victory.

Gohar will face defending champion El Welily while El Sherbini will face Serme, who extended her unbeaten run to 12 matches, after recording a seventh straight victory over eight-time world champion Nicol David of Malaysia after a comfortable 11-9, 6-11, 11-6, 11-4.

"I've watched Nicol since I was six years old and I've learnt a lot from her," said El Sherbini.

"She's always difficult to play against – she fights for everything and never gives up.

"It is always very tough and she brings the best out of me but I am happy that I am through."

The event is due to conclude on Wednesday (March 1).