Gai Waterhouse and Tommy Berry added the finishing touches to a spectacular day when Cosmic Endeavour cruised to victory in the Sapphire Stakes at Randwick on Saturday.

The success came on top of a Group One double with Diamond Drille in the Queen Of The Turf Stakes and The Offer in the Sydney Cup, as well as a minor placing by Carlton House in the Queen Elizabeth Stakes.

"It's amazing how you step with a really light step when you have these winners. You feel fantastic," Waterhouse said.

"I was delighted even with Carlton (House). I thought he was glorious in defeat."

Tommy Berry described the day as the most significant of his career, given it came just a couple of weeks after the sudden death of his twin brother and fellow jockey Nathan.

His on-track efforts resulted in him tying with James McDonald as the most successful jockey over the two days of The Championships with the pair joint winners of the inaugural Nathan Berry Medal.

"Nathan's medal, that means more than any Group One," Berry said.

"It's probably the biggest day of my career given the circumstances. I don't think I'll ever be able to top a day like this."

Cosmic Endeavour ($8) led throughout to score by two lengths over Avoid Lightning ($11) with another half length to Belle De Coeur ($31).

Waterhouse said the winner could head to the Dark Jewel Classic at Scone or a race during the Brisbane winter carnival.