With 21 consecutive wins in a glorious run that dates back to May 2015, champion mare Winx is, at the moment, unbeatable.

Of those victories, 14 have been at Group 1 level, and on Saturday afternoon at Moonee Valley, she has the chance to join the great Kingston Town as the only three-time winner of the Cox Plate – widely regarded as Australia’s best horse race.

But, believe it or not, there was a time when Winx was beatable. In the Hunter Valley in New South Wales, there’s a six-year-old mare, now retired and in foal to champion sire Snitzel, who actually had the measure of Australia’s darling of the turf.

Her name is First Seal, and in seven meetings with Winx, she finished ahead of her on five occasions, winning three races.

“My filly was the very dominant three-year-old, she had the wood over Winx,” First Seal’s trainer John Thompson told The New Daily.

“It was a long time ago. As Winx has got older, she’s just got better with age.”

Thompson rates Winx alongside the likes of Phar Lap, Kingston Town, Makybe Diva and Black Caviar.

He wishes the mare was made to work harder for her wins, like some of the stars of yesteryear, but claimed she’s simply too good.

“She’s a super mare, definitely one of the best horses we’ve seen,” he said.

“She’s very dominant. I would have liked to have seen another horse come along and challenge her; [but] there’s nothing.

“She’s beaten good horses and beaten them easily. Sunline [a dual Cox Plate winner], for example, was beating Lonhro and Northerly and horses like that.

“You’d like to see her take on another champion and beat her.”

That challenge may come next year, with Winx’s trainer Chris Waller admitting the wonder mare is a strong chance to take on the world, away from her backyard, in 2018.

Of that prospect, Thompson said: “It would be very exciting. She’s got nothing left to prove in Australia.

“For her to run at Royal Ascot [in England] then go on to the Prix de l’Arc de Triomphe [in France] and prove to the world that we’re not just a country with good sprinters, we’ve got stayers and middle-distance horses as well.”

At $1.15 for the win, Winx will start the shortest-priced Cox Plate favourite since Phar Lap’s win in the race in 1930.

And Thompson believes the result is a formality.

“Nothing can beat her on Saturday,” he said.

Ahead of her tilt at a third Cox Plate success, Winx boasts 25 wins from 31 starts, and prize money of $13.8 million (second on Australia’s all-time list behind three-time Melbourne Cup winner Makybe Diva, who amassed $14.5 million).

From 21 starts, First Seal won one Group 1 – that victory coming in the 2014 Flight Stakes at Randwick when she finished three lengths ahead of second-placed Winx.

“That was a career highlight, to win a big Group 1 at Randwick,” Thompson said.

“She was brilliant that day.”

Sadly, for Thompson and First Seal’s owners, injury prevented their heroine from reaching the same heights as her arch-rival.

“She [First Seal] was sound as a three-year-old, but when she turned four she got a few injuries and was never the same after that,” Thompson explained.

Like many racing stories, it is a case of what might have been.

“That’s racing isn’t it? Unfortunately, injuries are a part of racing; it’s something we would all like to take away,” Thompson added.

“I guess it’s something we will never know [how good she could have been].

“She’s probably the best horse I’ve trained so far. She was just all class.

“She was a big, strong filly and very powerful at that age [three].”