The previously-unbeaten Lah Ti Dar had to make do with minor honours in the William Hill St Leger as Kew Gardens provided Aidan O'Brien with a sixth victory in the world's oldest Classic.
Having made a spectacular return from an enforced summer absence in the Galtres Stakes at York last month, Lah Ti Dar was earlier this week given the green light to take on the boys on Town Moor and soon shot to the head of the betting.
With her half-brother Too Darn Hot firming up as ante-post favourite for both the 2000 Guineas and Derby with victory in the Champagne Stakes a little over half an hour earlier, Lah Ti Dar was all the rage to provide John Gosden, Frankie Dettori and owner-breeders Lord and Lady Lloyd Webber with a big-race double.
But Kew Gardens had not read the script.
As stablemate Nelson did the donkey work in front, the 3-1 chance travelled powerfully in the midfield under Ryan Moore, with 7-4 favourite Lah Ti Dar always in his wing mirrors.
The latter looked all at sea for a few strides after straightening up for home, but it is to her credit that she regained her composure to chase down Kew Gardens after he hit the front racing inside the final furlong.
Steadily the filly closed the gap, but Kew Gardens was not for catching and passed the post with a shade over two lengths in hand.
O'Brien was on hand to welcome Kew Gardens back into the Doncaster winner's enclosure, before he and Moore darted across the track to catch a flight to Leopardstown.
Before making his sharp exit, O'Brien said: "We couldn't be happier with him. He's a horse that's progressed lovely.
"We always thought he was a horse that would stay well and we thought the distance would suit him.
"He has a lot of class and we're over the moon really."
Gosden was proud of Lah Ti Dar's performance in defeat.
He said: "She ran a great race and as Frankie said, that's the first real race of her life. She's only ever seen about one horse before today.
"We'll freshen her up and go for the fillies' and mares' race on Champions Day at Ascot and then put her away for next year. That's the plan."
There were no such problems for Too Darn Hot, who came through his Group Two assignment with flying colours.
The Champagne Stakes looked a warm race on paper, but the prohibitively priced 4-11 favourite looked in a different league as he dismissed his rivals in emphatic style.
A visibly impressed Dettori said: "That was very special. What he did between the three and the one blew me away.
"I guess the next step is a Group One, but he is very talented."
Too Darn Hot's end-of-season options include the Darley Dewhurst Stakes at Newmarket on October 13 and the newly-named Vertem Futurity Trophy back at Doncaster a fortnight later.
"I'm happy with him and he did everything right. He quickened up from a long way back - he's a young, talented horse," said Gosden.
"He's in the three Group Ones in October and there'll be no decision (on which one he runs in) for 10 days."
Mustashry (5-2 favourite) knuckled down to win the Group Two Park Stakes for Sir Michael Stoute and Jim Crowley.
The Charlie Hills-trained A Momentofmadness (25-1) blitzed his rivals in the William Hill Portland Handicap in the hands of William Buick.