Xavi's Al Sadd beaten in quarter-final first leg
Al Nassr, who qualified for the quarter-finals for the first time, missed star striker Abdelrazzaq Hamdallah through injury.
But nevertheless they made most of their chances to clinch the win in front of a huge crowd at the King Fahd International Stadium in Riyadh.
The hosts enjoyed the upper hand early in the match and came close to scoring in the 14th minute when Abdulrahman al-Dawsari broke free and passed to Saleh al-Abbas, whose shot hit the upright.
With the pace picking up, Al Sadd began to make inroads and broke the stalemate in the 21st minute.
Abdelkarim Hassan's pass from the left was fumbled by Hassan al-Haydos but the ball fortuitously fell to Ali Asadalla, who scored with a measured shot from the right into the top of the net.
The hosts kept looking for openings and built up pressure, finding the equaliser a minute before half-time, thanks to a defensive lapse.
Giuliano's corner caught Al Sadd napping and al-Dawasri was quick to pounce on the ball and shoot home from close range.
Al Nassr could have gone ahead immediately after played started in the second half but Al Sadd goalkeeper Saad al-Sheeb brought off a fine reflex save off a powerful shot from Fahad bin Jumayah.
While the Al Sadd attack led by Akram Afif did cause jitters for the hosts, they couldn't find a way to get past the defence.
Al Nassr found the winning goal in the 72nd minute, this time Giuliano turning from provider to scorer.
Moroccan Nordin Amarabat instigated the move, crossing from the left for Feras al-Biraikan, who in turn headed the ball towards Giuliano.
The Brazilian made no mistake with a header of his own, his sixth goal of the tournament.
Al Sadd will now meet Al Nassr in the second leg on September 16 in Doha, hoping their away goal will stand them in good stead as they chase a second straight semi-final spot.