- Mohamed Magdy (88')
Mohamed Afsha's 88th minute rebound, after he had initially struck the woodwork, took a wicked deflection to win the game for the Egyptian club and set up a dream match for them against the European champions.
Afsha hit a speculative effort from distance that looped over Seattle goalkeeper Stefan Frei and dipped onto the crossbar, bouncing right back into his path and allowing him a volley that Alex Roldan steered past his own goalkeeper as he stuck his foot out to block the shot.
"I thought we were good. I thought we were evenly matched. A couple of chances. But the deflection on the goal, it's unfortunate," a dejected Seattle coach Brian Schmetzer said.
Al Ahly, competing at an eighth tournament, now meet Real Madrid in Rabat on Wednesday, which follows Tuesday's other semi-final between Flamengo of Brazil and Al Hilal of Saud Arabia.
Asian champions Al Hilal won earlier on Saturday against home team Wydad Casablanca on post-match penalties after a 1-1 draw.
It was a heart-breaking finish for Seattle, the first Major League Soccer team to compete at the Club World Cup, and still in their preseason before their league campaign kicks off later this month.
"They put everything into the game. They put everything into preseason," Schmetzer added.
The game had few chances although the Egyptians, who were semifinalists at the last Club World Cup in 2021, enjoyed much possession.
- Anthony Taylor