Trained by Mark Johnston and ridden by weighing-room stalwart Joe Fanning, the 13/2 chance was always prominent and powered home unchallenged, with Stradivarius fading to fourth after gallantly trying to make up ground under Frankie Dettori once getting a clear passage.
Princess Zoe was second at 28/1, with Spanish Mission third at 7/1.
Fanning sat second throughout as Amhran Na Bhfiann set steady fractions at the head of affairs, while Dettori on Stradivarius was happy to let the race unfold in front of him.
Fanning kicked clear with over two furlongs to run, just before the field turned into the straight, and as the runners bunched up Dettori found a wall of horses in front of him on the favourite.
Subjectivist - so impressive in the Dubai Gold Cup last time out and a Group One winner in France before that - took three lengths out of the field and was never likely to be found out for a lack of stamina.
As he kicked clear Amhran Na Bhfiann was weakening rapidly - right into Dettori's path - and all of a sudden Stradivarius was up against it.
Tony Mullins' mare Princess Zoe came out of the pack to chase Subjectivist and although Dettori tried valiantly to weave his way through, he found himself with too much to do.
Subjectivist (13-2) had five lengths to spare over Princess Zoe, with Spanish Mission a further half-length back in third, just ahead of the 5-6 market leader.
Johnston had won the race previously with Double Trigger in 1995 and Royal Rebel in 2001 and 2002, and had been second in numerous big races to Stradivarius with Dee Ex Bee and Nayef Road.