Australian referee Chris Beath's first-half sending off of Al Nasser's Ali Lajami has helped Al Hilal advance to their second Asian Champions League final in three seasons.
Salem Al Dawsari's deflected second-half strike settled the semi-final between the Saudi Arabian rivals 2-1 at a packed King Saud University Stadium in Riyadh.
Al Hilal will contest the final in Riyadh on November 23 against South Korean opposition - with defending champions Ulsan Hyundai to take on Pohang Steelers on Wednesday for a place in the decider.
Moussa Marega gave Al Hilal the early lead before the Lajami red card in first half added time handed given Leonardo Jardim's team the extra-man advantage.
However, Anderson Talisca levelled five minutes into the second half before Al Dawsari's late match winner.
Al Hilal's attempt to successfully defend their title last year ended in expulsion from the competition in the group phase after a COVID-19 outbreak within their squad left them unable to field a team for a game against Shabab Al Ahli.
But there have been few problems for the three-time Asian champions in this year's campaign and Marega gave them the perfect start against their cross-town rivals.
In the 17th minute, Al Nassr lost possession inside the Al Hilal half and within seconds the ball was in the net as a series of slick passes ended with Bafetimbi Gomis playing Marega in on goal and the Malian's deflected shot looped over keeper Waleed Abdullah.
Al Hilal's hopes improved further when Al Nassr weere reduced to 10 men when Beath issued a straight red card to Lajami for a lunge that caught Marega high.
Talisca equalised for Al Nassr when he met Abdulfattah Asiri's corner with a firm header to keep his side's hopes of a first Asian Champions League final appearance alive.
Those dreams were dashed in the 71st minute, however, when Al Dawsari's strike from inside the area took a heavy deflection off Al Nassr captain Abdullah Madu.
Australian Associated Press