Strewth! The Wonder from Down Under nearly became the Blunder from Down Under as unbeaten Australian mare Black Caviar just held on for a nerve-tingling 22nd consecutive win.

Jockey Luke Nolen admitted to a rookie error as he dropped his hands close to the line and was nearly caught in the Diamond Jubilee Stakes.

An army of Aussie followers descended on Royal Ascot, but the Antipodean cheers among the 77,000 crowd turned to gasps as the mare almost surrendered her modern-day record unbeaten run.

"Relief, relief relief," replied Nolen, 32, when asked what his emotion was after passing the winning line.

He admitted his "mind had been blown a bit" by intense media focus on the horse and he knew the headlines back home would focus on his ride as much as the landmark victory.

"I underestimated the gruelling six-furlong straight. Because it was such a test for her, she pulled up very quickly and it took me by surprise," he said.

"I didn't have as much experience as other riders here and just let her coast. It was an error every apprentice is taught not to do but I got away with it today.

"I just let her idle at the finish and maybe the big engine just shut down.

"She's now 22 from 22 and that's what it should be all about, it would have been a travesty if she had lost today. Imagine if she had got beat, I'd have probably been stabbed.

"She wasn't her usual self today. On Tuesday morning it felt like she was in career-best form, but until you put them under race pressure, you don't know how they have taken the trip over."