The partnership of Aidan O'Brien and Christophe Soumillon combined to win the opening two Group 1 races at ParisLongchamp on Prix de l'Arc de Triomphe day.

Diamond Necklace came from off the pace to win the Qatar Prix Marcel Boussac while Puerto Rico made all the running to win the Prix Jean-Luc Lagardere. Both two-year-olds won comfortably.

The unbeaten Diamond Necklace, who is by St Mark’s Basilica, was the 11/10 favourite in a field of nine as she aimed to maintain her flawless record when stepped up to Group 1 level.

Under a patient ride she did so with little fuss, travelling in mid-division until the home turn before mounting a challenge and quickly taking up the lead to triumph by a length from Green Spirit without being fully extended.

Aidan O'Brien said: “We’re absolutely delighted with her, and the fact she’s by St Mark’s Basilica makes it even more special. Over the past two months, his progeny have been improving week after week. Remember, he didn’t win his first Group race until the Dewhurst Stakes on October 10th, and we all know what he did at three. He’s clearly passing on his own profile — they’re not early types.

"I was a bit concerned that Diamond Necklace might still be a baby for this race, and I spoke to Christophe about it. He advised running her and then giving her a quiet winter. She’s a filly who could aim for the 1000 Guineas and then the Oaks, as I believe she’ll stay a mile and a half. She’s one of our best two-year-olds."

Diamond Necklace was bought as a yearling in Deauville for €1.7 million. Her dam Prudenzia (by Dansili) had already produced several champions, including Magic Wand (by Galileo).

She was bred in Normandy by Haras des Monceaux (in partnership with Skymarc Farm, the operation of the late Lady O’Reilly).

Henri Bozo, manager of Monceaux, said: "It was quite bold to send a mare of that calibre to a young stallion, just starting his career. But it paid off. We like to send older mares to younger stallions. I try to avoid pairing older mares with older stallions. The bloodline of St Mark’s Basilica — his power, depth and turn of foot — made us want to try it. Together with Patricia Boutin, who managed Lady O’Reilly’s interests, we decided to send her to that stallion.

"The information I got from Coolmore was that they thought Diamond Necklace would be better at three than at two. So this is great. It’s a family that usually peaks in midsummer of their three-year-old season, and they tend to prefer good ground. It’s not a family of big-framed horses — and she herself isn’t very big. We sold her sister this year at Deauville; she might have been a bit taller.”

Made all

Puerto Rico paid a further compliment to his late sire, Wootton Bassett, when making all the running to land the Qatar Prix Jean-Luc Lagardère. Wootton Bassett, who won this race himself, is also the sire of the runner-up Nighttime. The Aga Khan-bred Rayif went off the short-priced favourite and took third.

Repeating the tactics which saw him win the Group 2 Champagne Stakes at Doncaster last month, Puerto Rico went straight to the front and quickened strongly in the straight for an untroubled victory.

Aidan O'Brien said: “When we stepped him up to seven furlongs last time out, he really progressed. He’s a beautiful horse — big, strong, mature and with plenty of speed. Camille Pissarro [winner of this race in 2024] was also a big, powerful, dark horse — just like Wootton Bassett — and this one is the same: big, strong, dark, and very fast. Wootton Bassett himself had tremendous speed, and this colt has just as much of it.

"Christophe said he’s a very fast horse, a real miler. He added he won’t go beyond that trip, but he has an awful lot of pace. (…) I probably ran him over trips that were a bit too short earlier on, because he was showing so much speed."