There's nothing worse than punters losing their shirts at the track, unless its a jockey who has lost his pants trying to win a race.

In one of the more risque and embarrassing moments in Australian horse racing, leading jockey Blake Shinn finished the opening event at Canterbury giving racegoers the ultimate bum steer.

Shinn's trousers gave way soon after the start and he bared all to the racing world as television cameras zoomed in on Thursday's finish.

But showing the composure that helped him win the 2008 Melbourne Cup, Shinn managed to guide his mount Miss Royale into second place, ahead of the aptly named third placegetter Modesty.

Shinn became an instant social media hit with photos of his predicament doing the rounds on Twitter.

Deputy chairman of stewards Greg Rudolph said he had never seen anything like it on a racecourse.

"Normally we report gear malfunctions in races but we left that one alone," Rudolph said.

Although he was the butt of jokes from punters, Shinn was happy to join the banter once he completed his riding commitments by booting home Eisenhower to win the last race.

"Usually I come to the races focused and determined," Shinn said.

"I didn't realise people thought I was that cheeky."