Winx's rating as the world's best racehorse is under threat.

A runaway French Group One win has Japanese star A Shin Hikari poised to usurp Winx and America's California Chrome when the next set of world rankings are released.

A Shin Hikari posted a 10-length margin in winning the Prix d'Ispahan at Chantilly on Tuesday, prompting Australia's international racing expert Greg Carpenter to anoint the horse as a global leader.

"Now, there's no doubt that when the World's Best Racehorse rankings are released in the second week of June, that Winx and California Crome will be surpassed by the performance of A Shin Hikari last night," Carpenter told Melbourne radio station RSN.

A Shin Hikari won last year's Hong Kong Cup in December.

And taking into account the opposition and margin at Chantilly, Carpenter said mathematically A Shin Hikari could have run to mark in the mid-130s.

Winx and California Chrome have a rating of 126.