The decision to back Saigon Tea up after her Rosehill win a week earlier proved a masterstroke when the mare took out the Listed Christmas Cup at Randwick.

Her win gave premier Sydney trainer Chris Waller a treble from the first three races on Saturday and helped ease the stress of a painful week.

Waller was fined $30,000 and Junoob stripped of his win in the Group One Metropolitan after an inquiry into an anti-bleeding medication in his system in a raceday sample.

Stewards found the positive result was due to human error and Junoob had been mistakenly given the medication.

"It has been a tough week," Waller said.

"But the only thing to do is get back on with things."

After Saigon Tea won over 1800m last week, the Christmas Cup (2400m) was not in Waller's thinking.

But heavy rain in Sydney persuaded him to give her a chance with all bar one of her previous six wins on wet tracks.

"When the rain came down on Sunday and Monday, I started to think about it," he said.

"It definitely played a major part in her racing here today.

"She didn't lose any weight and she is a 2400-metre horse so she was fit enough to have a quiet week."

Punters thought the back-up was a good idea with the mare the $2.50 favourite.

Glyn Schofield timed his run to perfection, bringing her from back in the small field.

She was challenged by Terai but beat her rival off to win by a long head.

The two were in a race of their own with Metaphorical ($3.70) a distant 8-1/2 lengths third.

Waller won the first two races with Dupe'Em and Beyond Thankful.