Ahba's task was, at the outset, a difficult one and it got worse just 12 seconds in.
Following the kick-off, Sultan Al Ghannam fed Sami Al Najei and the midfielder made no mistake to open the scoring for Al Nassr earl on. It was the fastest goal in the history of the King's Cup.
The early stages were intense, and before the half-hour mark the visitors came close to equalising. Saleh Al Jamaan took advantage of a defensive error by Rudi Garcia's men, but Álvaro González was able to recover.
Cristiano Ronaldo, again a starter for Al Nassr, was looking for a goal and found an opportunity on the quarter-hour mark, with Mohammed Maran coming close to adding to his tally.
Maran failed to do so, but Abdullah Al Khaibari managed to find the net. With 20 minutes played, Ghislain Konan crossed from the left side of the attack and the midfielder position himself well in the penalty area to score with his left foot first-time.
Comfortable in the game and on the scoreboard, the Riyadh side slowed their pace and only managed to find the net again five minutes before the break when Ronaldo received the ball in a central area, flicked it on with his left foot and shot wide.
At half-time, there was little doubt about the final outcome and any remaining doubts were dispelled as the match restarted. In the 48th minute, after a short corner from the right, Maran anticipated the opposing goalkeeper and then shot into the empty net.
Ahba did not react until the 65th minute, when Abdulfattah Adam, who had just come on, headed the ball into the path of Nawaf Al Aqidi, who saved well.
The response was swift and, a few minutes later, Ali Al Hassan was given space in the centre of the park, only for Devis Epassy to deflect his shot onto the post to prevent Al Nassr's fourth goal.
Then Saad Al-Salouli gained a foothold in the middle of the park, Al Aqidi saved well, and Adam reduced the deficit on the rebound.
Nevertheless, Al Nassr kept control of the match, managing it until the end without great difficulty and sealing their ticket to the semi-finals, where they will face Al Wehda.
In a lacklustre afternoon, Ronaldo was replaced by Talisca, who returned to the competition after an injury absence.
Al Nassr and Ahba meet again on Saturday in Riyadh in the league.
