The John Gosden-trained champion stayer Stradivarius had to work hard to scoop a £1million bonus at York while Alpha Delphini squeezed home by a nose in the showpiece sprint.
Stradivarius added the Group Two Lowther Stakes to his previous wins this season in the Ascot Gold Cup and Goodwood Cup to land his owner-breeder Bjorn Nielsen a seven-figure windfall.
Frankie Dettori, who 24 hours earlier had been on board Mark Johnston's record-breaking 4,194th winner, was again the man in the hot seat.
The 4-11 favourite had enough class to see off the challenge of 14-1 chance Count Octave with Idaho at 7-1 in third.
"I think it must have felt like he's just done 30 rounds with Joe Frazier and Muhammad Ali but he got here and did it in a race not run to suit," Gosden said.
"It's a phenomenal achievement from a gritty, tough horse. He wasn't at his sparkling best and he'll have a nice freshen up and rest. He deserves it.
"Full marks to the owner, he's been trying to breed a Derby winner for years and he ends up with a Cup horse!
"But seriously, he's passionate about breeding and puts a lot of time and effort into it, so he deserves it.
"It's an extraordinary achievement. The horse has a lot of determination, but also a lot of class."
Reflecting on the year, he said: "The highlight was definitely Ascot, that was a terrific race, we never knew if he'd stay or not.
"After the first leg we were only thinking of Ascot, after that then it (bonus) became a real possibility, then of course, after Goodwood we were only ever going to be thinking of it."
The inimitable Dettori quipped: "Show me the money!"
Yet again the five-furlong Coolmore Nunthorpe Stakes produced a memorable finish, as two Yorkshire-trained runners, Alpha Delphini and Mabs Cross, were separated by just a pixel at York.
Just 12 months on from the drama of Frankie Dettori's premature celebrations on Lady Aurelia only for Marsha to get the verdict, Graham Lee and Tom Eaves respectively were more restrained on crossing the finish line.
The truth was, of course, that there was so little between them that neither had a clue who had won as they flashed past the winning line together.
Initially seasoned watchers were convinced Mabs Cross had provided Michael Dods with a third win in four years after Mecca's Angel in 2015 and 2016, but the longer it went on the more a dead-heat became a possibility.
When the result was announced over the tannoy, Bryan Smart jumped for joy, as Alpha Delphini, who returned at 40-1, joined half-brother Tangerine Trees as a Group One winner.
Hot favourite Battaash yet again flopped at York, finishing only fourth, while to rub salt into Eaves' wounds he was given a four-day whip ban.
"That was the longest five minutes of my life!" said Smart. "I backed him this morning, I had a tenner each-way at 80-1 because I thought that was an insulting price.
"I knew I had him the best he'd ever been, I'd trained him for this race as it was one I'd always wanted to win.
"I'd told the wife months ago that he was going to be absolutely spot-on for this, he was just coming right.
"We've put him in the Abbaye and there's a good chance he'll go for that. We did have the Beverley Bullet as a back-up, but we can skip that now."
There is just no keeping Dettori out of the headlines, though, and the veteran Italian showed once more that whether a race is over two miles or six furlongs, he is just as effective, clinching a double on Emaraaty Ana (5-1), a spare ride in the Al Basti Equiworld Gimcrack Stakes.
Titus was an emphatic winner of the Sky Bet Handicap.
Declan Carroll's charge was an 8-1 shot on the back of finishing fourth in last month's John Smith's Cup on the Knavesmire, form that has been well advertised since with runner-up Thundering Blue subsequently winning a Group Two and finishing third in Wednesday's Juddmonte International.
Titus travelled into contention with remarkable ease in the hands Ger O'Neill, with the 5lb claimer sat motionless while his rival jockeys rowed along halfway up the home straight.
The four-year-old could be called the winner a long way out and once given his head, he swiftly put distance between himself and his rivals, passing the post with four lengths in hand.
Mister Belvedere was best of the rest in second ahead of Kelly's Dino and Pacify in third and fourth respectively.
Carroll said: "He's had some good runs in some very good races. He was going up in trip today and has done it very well. We knew he'd improve for going up in trip. Ger rode him very well. He's a good kid."
Considering future targets, the trainer added: "There's a handicap at Leopardstown I was looking at, but we'll just see. The £1million Ebor next year sounds very good!"
Commanding Officer opened his account at the third attempt in the British Stallion Studs EBF Convivial Maiden Stakes.
Karl Burke's youngster finished fourth on his debut here in late July before filling the runner-up spot at Haydock a fortnight ago.
He was sent off at 11-1 for what is traditionally a strong event and knuckled down well to see off Indomitable by half a length.
Burke said: "That was great. He's has a bit of a kink to him, but he's a lovely colt. He's more a horse for next year, to be honest.
"I think we'll stick to seven furlongs for the time being and he is in the Champagne Stakes at Doncaster. If he bounces out of this well that will be an option.
"He'll definitely get a mile and may even get a mile and a quarter. He's a big, strong horse and we're under no pressure with him at the moment."
