Superstar colt Pierro returned to Golden Slipper day triumphant to increase his unbeaten streak in Sydney but was made to work harder than expected in the Group One George Ryder Stakes.

The colt, labelled by trainer Gai Waterhouse in the excitement of the victory celebrations as "the best horse we've seen in Australia for 50 years", notched his fifth Group One and his second at weight-for-age against older horses with a determined long neck win over New Zealander King Mufhasa.

The victory moved Pierro to odds-on favouritism for the Doncaster Mile (1600m) at Randwick in two weeks.

For jockey Nash Rawiller it was a happy return to the saddle of last year's Golden Slipper winner after partnering stablemate More Joyous in the Canterbury Stakes two weeks ago when Jim Cassidy steered Pierro to victory.

Cassidy said Pierro was the best he'd ridden, a position the colt also holds in the pecking order of top-class gallopers Rawiller has partnered.

Pierro ($1.35) didn't have the best run in transit as he was wide and midfield and Rawiller admitted to concerns as the colt "dipped and dived" in the slow going.

But when it came down to the fight the three-year-old was able to prevail and make it 10-straight wins in Sydney.

He wore down a gallant King Mufhasa ($91) with Shoot Out ($13) finishing off well to be three-quarters of a length away in third.

"I think he's getting better but I don't think we saw the best of him today in the conditions," Rawiller said.

"King Mufhasa gave a bit of a kick and I thought it was going to be a dog fight. But you wouldn't want to be on any other horse.

"He just pulls out that neck when you need it."

The win capped another memorable day at the track for Waterhouse who won the Golden Slipper with Overreach 45 minutes earlier.

But Waterhouse said victory from the horse she rates as the best she's trained was something special.

"I very rarely get goosebumps watching races, and I've watched a few top-class horses, but today I really got goosebumps," she said after the Ryder.

"He's a special horse. He's a sexy horse. He's the best."

The run of King Mufhasa delighted trainer Bruce Wallace after the gelding underwent throat surgery after his last start.

"It's the first time he's been able to breathe and the first time I've seen the real Mufhasa," he said.

King Mufhasa will now head to Hong Kong for the Champions Mile.