'The Wonder from Down Under' narrowly landed the Diamond Jubilee Stakes by a fast-fading head and neck from Moonlight Cloud (5-1) and Restiadargent (40-1) for her 22nd consecutive victory.
Nolen was the first to admit his mistake aboard the 1-6 favourite and Australia's most famous horse since 1930 Melbourne Cup winner Phar Lap.
"It was an error that every apprentice is taught not to do and I got away with it today," Nolen, in confessional mode, said.
"I probably just underestimated the testing track.
"It is going to overshadow what was a very good win. They are going to talk about my brain-fade rather than the horse's fantastic effort."
Black Caviar took the lead at halfway and moved clear of the field but was caught in the closing stages of the six-furlong sprint, leaving the thousands who had flocked to Ascot to see her, with an anxious wait for the official result.
There were gasps of relief when the photo finish result was announced.
"You have only got to win by a quarter of an inch. That's what we were prepared to come here and win by. We have got the job done," said Black Caviar's trainer Peter Moody.
Britain's Queen Elizabeth II came down to the paddock afterwards to admire the mighty mare and offer her a pat of congratulations.
Moody said it was quite overwhelming to meet the Queen, adding: "There is no doubt that Her Majesty is certainly a horse lover - the two queens of Australia maybe?"
Black Caviar's 11,000-mile trip from Australia wearing a specially designed equine compression suit had clearly taken its toll and any arguments about her being better than the world's highest ranked racehorse, Frankel - who won Tuesday's Queen Anne stakes by 11 lengths - rang hollow afterwards.
About 5,000 Australian racing fans poured into Royal Ascot to watch the much-hyped race, which was also shown live in Melbourne's Federation Square.
The Melbourne Cup has always been known as the race that halts a nation for the day but on Saturday it was a horse on the other side of the world who did just that.
3-1 favourite Sea Moon won the Hardwicke Stakes by three-and-a-quarter lengths from Melbourne Cup one-two Dunaden (9-2) and Red Cadeaux (9-1).
Irish 33-1 hope Dandy Boy claimed the Wokingham by a length-and-a-quarter from Waffle and Hawkeyethenoo.
11-4 favourite Simenon won his second race of the week in the Queen Alexandra Stakes. Shahwardi in second was seven lengths back with Romeo Montague third.
Frankie Dettori rode Tha'ir to glory in the opening race of the day, the Chesham Stakes, by two-and-a-quarter lengths from Cruck Realta. Lovely Pass, like Tha’ir, is from the Godolphin stable.
Favourite Camborne won the Duke of Edinburgh Handicap.