World number one sprinter Nature Strip was far too good for his King's Stand Stakes rivals on the opening day of Royal Ascot.
The 9-4 shot drew right away from the 16-runner field in the closing stages – and crossed the line four-and-a-half lengths ahead.
Khaadem, who unseated jockey Jamie Spencer after the stalls opened, accompanied the international star across the line.
Twilight Calls (11-1) was best of the British contenders in second, while rank outsider Acklam Express (200-1) finished third.
Speaking after the race, jockey James McDonald described Nature Strip as "an absolute freak of a horse". He said: "That was incredible, the team has done a marvellous job.
"He's an absolute freak of a horse and would have silenced a few of his critics with that race. To come back and win a Group 1 here is up there."
America's big hope Golden Pal, backed into 15-8 favourite before the start, missed the break and failed to beat a rival home.
McDonald said he originally did not know Khaadem was without his jockey as they charged for the line.
"With the riderless horse, I didn't even realise he was riderless and I thought 'how has anything gone with him?' he added.
"At the two-pole I was thinking 'are you going to come?' to the American horse, but he didn't."
Nature Strip was the first Australian-trained runner to win at the meeting since Black Caviar in 2012.
The mare took the Diamond Jubilee Stakes, now renamed after the Platinum Jubilee in honour of the Queen's 70 years of service.
Nature Strip is 5-2 (from 6-1) to follow up in that race on Saturday, where he will be joined by stablemate Home Affairs.
