After a goalless first leg at Loftus last week, Sundowns fell behind in the first half after a stunning strike from Taher Mohamed but scored the all-important equaliser in the last minute of regulation time when Al Ahly defender Yasser Ibrahim put the ball into his own net under pressure.
The South Africans started the game well and carved out the first opportunity when Lucas Ribeiro Costa played in Tashreeq Matthews, but the forward put his effort wide.
Al Ahly are giants of African football though and have won the continent’s most prestigious club trophy a record 12 times and started to flex their muscles in front of their passionate fans.
Midway through the first half Sundowns lost possession and the Egyptian club pounced and launched a quick attack that saw Mohamed in space down the right and the forward launched a bullet effort that beat visiting goalkeeper Ronwen Williams and into the top corner.
The home team was now smelling blood and came close to doubling the lead after 33 minutes when Emam Ashour tested Williams from a tight angle but the Bafana Bafana shot-stopper did well to save.
There was huge controversy just after the hour mark when Ribeiro appeared to have been fouled in the box by Ibrahim, but the referee denied the Sundowns appeals.
The on-field official was then summoned by the VAR official and sent to the screen to check his decision, but the referee decided to stick by his original call.
Sundowns knew an equaliser would be enough and coach Miguel Cardoso sent on forwards Iqraam Rayners and Peter Shalulile with 15 minutes of the contest remaining.
The duo certainly caused the home defence problems with their presence and the visitors pressing in the final stages.
Al Ahly looked to have done enough but in the final minute Sundowns launched a ball into a crowded box that hit Rayners and a back-tracking Ibrahim was unfortunate to put the ball into his own net from close range.
The goal sparked wild celebrations from the visitors while silencing the huge crowd.
The South Africans then negotiated seven minutes of added time to book their place in the CAF Champions League final.