Coach Xavi punched the air in delight as the 2011 continental champions put on a commanding home performance to secure a 4-3 aggregate victory and another shot at continental glory.
Al Sadd's star striker Akram Afif dazzled throughout. He scored the first goal in the 26th minute with a simple header from close off a delectable chip from the left by South Korean Nam Tae-hee.
The home joy was short-lived, however, as Al Nassr's star striker Abderrazak Hamdallah equalised in the 33rd minute.
After he was fouled just outside the box, the Moroccan hit the free-kick, which took a deflection from former Atletico Madrid player Gabi, completely wrong-footing Al Sadd goalkeeper Saad al-Sheeb.
There were close calls at both ends, before Al Sadd went ahead once again. Captain Hassan al-Haydos cracked a shot from outside the box off another Nam pass, with the ball dipping nicely into the top right corner beating Australian goalkeeper Brad Jones.
Both teams grew desperate as the minutes ticked by, but it was Al Sadd who had the momentum and looked like scoring any moment.
Sure enough that moment arrived in the 89th minute when al-Haydos released Afif with a perfect pass but the striker was brought down by Abdulla Madu when he was about to take the shot. The referee pointed to the spot
Al Sadd's Algerian star Baghdad Bounedjah, the top scorer in the tournament last season, converted with a powerful shot to Jones' right.
"We never lost hope after the first leg defeat and I had drilled into the players the importance of staying upbeat," Xavi said after the match.
"They lived up to their promise and now we are one step away from the final."
Xavi had said at his pre-match press conference that it was his ambition to win the AFC Champions League, having won four European Champions League titles as a player for Barcelona.
Al Sadd will next play the winners of Tuesday's match between Saudi sides Al Hilal and Al Ittihad.