Damian Alvarez created the first chance of note for the Tuzos, scorching forward in minute 14 to force a corner. Juan Carlos Cacho nodded off the crossbar from the resulting Christian Gimenez set piece and Gabriel Caballero's try was cleared off the line.
Though the first half ended scoreless and with Pachuca in complete control, the Tunisians headed into the locker-room with some reason for optimism after a pair of chances from teenage sensation Mohamed Amine Chermiti had Colombian keeper Miguel Calero looking nervous.
Sahel came out with a greater sense of purpose after the restart, but Pachuca kept up the pressure and even had a goal disallowed for offside. However, with just five minutes left to play, the African champions made the Mexicans pay for their profligacy in front of goal. On the end of a nifty counter-attack, Ghanaian Moussa Narry caught a wicked deflection off Leobardo Lopez to see his 35-yard shot slip past Calero and seal a semi-final place for Sahel.
The Tunisians will hope to keep up the form when they meet rampaging favourites and champions of South America, Boca Juniors of Buenos Aires, on 12 December.