Trained by Roger Varian and ridden by David Egan, Eldar Eldarov had plenty to do two furlongs from home as Haskoy hit the front, with the 9-2 chance looking for a run in what was something of a messy race.
However, when Eldar Eldarov - winner of the Queen's Vase at Royal Ascot and fourth last time out in the Grand Prix de Paris - found his path, he picked up in fine fashion for Egan, grabbing the lead inside the final furlong to win going away by two lengths.
Haskoy, who drifted towards the far rail at one stage and seemingly impeded Giavellotto, kept on for second with 11-8 favourite New London beaten a further half a length in third. Following the race the stewards deemed the interference Haskoy caused to Gaivellotto was serious enough for the filly to be placed fourth behind Marco Botti's charge, with New London promoted to second.
Varian - winning the race for the second time after Kingston Hill in 2014 - said: "I quietly thought he had a real big shout today.
"Not everybody was wowed by his run in France last time out, but the winner (Onesto) went and pushed Luxembourg all the way in the Irish Champion Stakes.
"He had a tough race that day which is why he didn't run again and he was only just getting going at the line in France. His run at Royal Ascot showed he had stamina in abundance and that race is proving a good trial for the Leger. He's also handled soft ground as a two-year-old.
"So I knew he'd stay and handle the ground, it was whether he was good enough.
"Sometimes the longer you do something the harder things get, so it gets more satisfying. I think we'd only been training three or four years when Kingston Hill won the Leger so this is a very sweet success.
"I think we see him as a Cup horse next season, he's blessed with stamina and has an admirable attitude. We brought him back to a mile and a half in France and he was only just getting going at the finish.
"If he stays sound we could have him for the next two, three or four years. I think he's very exciting.
"I'm delighted for David, you won't meet a nicer guy, he's genuine, hard working and gracious in defeat while not being obnoxious in victory."