Circus Maximus got the better of Terebellum in a pulsating climax to the Queen Anne Stakes at Royal Ascot.
Winner of the St James's Palace Stakes 12 months ago, the Aidan O'Brien-trained Circus Maximus went on to suffer a narrow defeat at the hands of Too Darn Hot in the Sussex Stakes before landing the Prix du Moulin and finishing fourth in the Breeders' Cup Mile.
The four-year-old was the 4-1 favourite to double his Royal Ascot tally, just ahead of John Gosden's recent Newmarket-winning filly Terebellum and the big two fought out a thrilling finish.
There was little to choose between the pair entering the final furlong and no quarter was given by either horse, with Ryan Moore aboard Circus Maximus and Frankie Dettori on Terebellum both in full flight.
As the line loomed, Circus Maximus just began to get the better of the argument and was a head in front where it mattered. Marie's Diamond was three lengths away in third.
O'Brien said from his Ballydoyle base in County Tipperary: "I'm delighted. That's him exactly - he's very tough. He quickened and then toughed it out, it's unbelievable really. Ryan gave him a brilliant ride.
"It's very exciting. Ascot is usually a very busy week for us, so it's brilliant today to see all the preliminaries and everything."
Motakhayyel won the opening Buckingham Palace Stakes at Royal Ascot, as the 2020 meeting got under way behind closed doors.
With no traditional royal procession before the start of racing and no spectators on course, it is a very different scene this year, but it was business as usual for trainer Richard Hannon and jockey Jim Crowley.
Sent off a 14-1 chance, Motakhayyel stayed on in fine style to run out a cosy winner over Jack's Point, who ran a huge race at 66-1.
Pyledriver sprang an 18-1 surprise for trainer William Muir and jockey Martin Dwyer in the King Edward VII Stakes.
Having had the benefit of a seasonal reappearance at Kempton two weeks ago, the Harbour Watch colt leapt into the Derby picture with a solid performance.
Sound Of Cannons took the field along and was five lengths clear at one stage with the second Arthur's Kingdom several lengths ahead of the rest of the field.
Dwyer made his move at the top of the straight and was soon in front. He kept up the gallop to win by two lengths from Arthur's Kingdom, trained by O'Brien and ridden by Dettori.
Mohican Heights was two lengths away in third place, with O'Brien's 10-11 favourite Mogul only fourth.
Dettori and John Gosden got off the mark for the week as Frankly Darling bagged a cosy success in the Ribblesdale Stakes.
A Newcastle maiden winner on the first day of the resumption of racing, Frankly Darling (11-8 favourite) made a seamless graduation to Group Two company as she easily accounted for Ennistymon, giving Gosden a 50th Royal meeting success in the process.
Despite the lack of a crowd, Dettori celebrated with his trademark flying dismount in the winner's enclosure.
Frankly Darling is now a 3-1 chance with Betway for the Oaks at Epsom on 4 July.