Richard Fahey's front runner, the outsider of the whole field at 25/1, edged out favourite Top Trip by the narrowest of margins.
At first glance it looked as if the first leg of British Champions stayers' series might have ended in a dead heat but Tony Hamilton's mount secured the second big race win for Yorkshire in as many days on the Knavesmire.
The market leader for French trainer Francois Doumen hunted the leader down in the final stages and Mickael Barzalona momentarily edged his mount into the lead.
But Glen's Diamond ralied and only a nose separated the pair with Royal Diamond (11/1) a further three-and-a-quarter lengths away in third.
Libertarian ran out the shock 33/1 winner of the Dante Stakes for trainers Elaine and Karl Burke, who train in Yorkshire.