The African champions will face Copa Libertadores title holders Fluminense of Brazil in the last four on Monday.
Al Ahly broke the deadlock in the 21st minute through left-back Ali Maaloul who converted a penalty which was awarded for handball by Al Ittihad defender Hassan Kadesh.
Marcelo Gallardo's team battled for an equaliser and also got a spot kick for handball by Al Ahly defender Mohamed Abdelmonem.
However, Al Ittihad's former Real Madrid striker Benzema failed to convert after his shot was brilliantly saved by goalkeeper Mohamed El Shenawy.
Al-Ahly increased their lead when Hussein El Shahat curled the ball into the net just before the hour mark from an assist by Kahraba, who three minutes later hit a cross-shot that Emam Ashour fired home after a quick counter-attack.
The Saudi champions, appearing in the tournament for the first time since reaching the semi-finals in 2005, ended their campaign with a last-minute consolation goal from Benzema.
That came just after Al Ahly's Anthony Modeste was sent off in the 90th having come on for Aliou Dieng minutes earlier.
The other semi on Tuesday sees European champions Manchester City against Asian Champions League holders Urawa Red Diamonds, who beat CONCACAF champions Leon 1-0 earlier on Friday.
