The joy of a momentous victory quickly turned to concern and dismay for trainer Chris Waller and the owners of Reliable Man when the horse broke down as he raced to the line in the Group One Queen Elizabeth Stakes at Randwick.

In the upset of the Sydney autumn carnival, Reliable Man, in only his second Australian start, trounced the star colt It's A Dundeel.

But 50m from the line Reliable Man, the highest-rated European racehorse ever imported into Australia, dipped badly before continuing to the line with jockey Hugh Bowman giving his signature winning salute.

"I didn't realise what had happened until after the line, otherwise I wouldn't have been carrying on like a pork chop," Bowman said.

He earlier told the horse's owners he felt the horse change stride 50 metres out, but hadn't realised there was a problem until they slowed to a trot.

For Waller, the Queen Elizabeth typified a rollercoaster week.

On Friday, the champion trainer went through the ordeal of an inquiry into positive swabs taken from three of his horses.

The inquiry totally exonerated him and he turned his attention to a race meeting he said he'd looked forward to more than most.

"I've never felt so good going into a day's racing," he said after the win, but before the injury to Reliable Man became apparent

"This is a serious horse, a really serious horse."

Within minutes though, Reliable Man, the 2011 French Derby winner, was loaded into the horse ambulance and taken from the track to the Randwick Equine Centre.

Vets later reported he had injured a tendon in his off fore leg.

After enjoying a cosy run until the 300m when Bowman made his winning move, Reliable Man ($12) beat It's A Dundeel ($1.28) by 2-1/2 lengths.

Happy Trails ($41) finished third, a further half length away.

For Murray Baker, the trainer of It's A Dundeel, the race also provided a major disappointment, although not on the scale of that surrounding Reliable Man.

The colt touted as the heir apparent to the No.1 spot in Australian racing raced at the back of the eight-horse field and jockey Michael Rodd set off after the leaders after passing the 800m.

But where he had cruised into the Australian Derby from the same point two weeks ago, It's A Dundeel came under hard riding almost immediately against the older horses in the Queen Elizabeth.

He appeared unlikely to run a place at the 300m, but stuck to his task.

"He had every show," said Baker.

"He was beaten by a better horse on the day."