An all-action first half saw four strikes hit the back of the net, with Toney converting in the seventh minute to hand Al-Ahli an early lead. Things got even better for the hosts when the former Brentford striker latched onto a long ball from the back to finish powerfully for his second goal of the night.
The visitors were shellshocked but were gifted a route back into the contest courtesy of a howler from goalkeeper Abdulrahman Al-Sanbi, who allowed Abdulelah Al-Amri's hopeful effort from distance to bounce through his legs.
With Ronaldo out of sorts, it was again the centre-back who struck for Al-Nassr to level proceedings. Marcelo Brozovic's out-swinging corner was met by the Saudi Arabian defender, whose firm header couldn't be reached by Al-Sanbi.
Toney made another telling contribution just before the hour mark, producing a brilliant flick to keep a set-piece alive and allow Merih Demiral to head in and make it 3-2.
Al-Nassr huffed and puffed in their pursuit of an equaliser but with Ronaldo and Joao Felix both off form they couldn't haul themselves level again. There was some late drama as both Ali Majrashi and Nawaf Al-Boushail were sent off in stoppage time, but that was inconsequential as Al-Nassr fell to a first league defeat of the season, offering Al-Hilal the chance to usurp them at the top of the table on Sunday.