Almost four decades after watching Kingston Town win one of his three Cox Plates, Japanese trainer Yoshito Yahagi has achieved an ambition to claim Australia's premier weight-for-age race.

Yahagi is the trainer of Lys Gracieux, the winner Saturday's $5 million Cox Plate (2040m) at The Valley, adding another feature win for Japanese horses this spring, a week after Mer De Glace won the Caulfield Cup.

"I was here when Kingston Town won back in 1982, it's been 37 years so I finally came back 'home'," Yahagi said through an interpreter.

"To win a Cox Plate means a lot to me.

"Thanks very much to Lys Gracieux, connections and to the Australian people."

Yahagi has won Group Ones in Japan and one in Dubai but rated Saturday's victory on top.

"For me personally, this is the best," he said.

The race became a possibility for Lys Gracieux after she won the Takarazuka Kinen in June, when ridden by Australian jockey Damian Lane who rode the mare again on Saturday.

The Cox Plate is the latest of Melbourne's big spring features to have been won by Japanese-trained horses.

Delta Blues and Pop Rock ran the quinella in the 2006 Melbourne Cup while Admire Rakti (2014) and Mer De Glace (2019) have been successful in the Caulfield Cup.

Yahagi was confident about Lys Gracieux's chances in Saturday's race but admitted he was concerned during the race when she was so far back.

She earned a $2 million bonus for the win after taking out the Takarazuka Kinen.