By Mathew Toogood

SYDNEY, Sept 1 AAP - Chris Waller won the opening race at Warwick Farm but his day didn't finish on the best note with boom colt Slater well beaten in his highly-anticipated return.

However, Slater's defeat provided a fairytale finish for apprentice Heather Poland who was having her final race ride on the Stephen Hill-trained Riebeek who took out ticketek.com.au Handicap (1100m).

Slater, who was sent out the $1.75 favourite, finished ninth and was found to be suffering from heart arrhythmia and displaying a poor post race recovery rate.

He has been ordered back to the barrier trials before he races again.

None of that mattered to Poland whose win on Riebeek brought a close to her riding career.

Poland finishes her apprenticeship this week and won't be taking out a senior jockeys' licence, opting instead for another role at the stables of Riebeek's trainer Stephen Hill.

"That was an excellent way to finish," Poland said.

Slater's jockey Jim Cassidy told stewards the colt was fractious in the barriers which was something he hadn't displayed before his previous win at Canterbury or any of his trials.

"I travelled nicely to the corner but as soon as I went to turn I was in trouble," Cassidy said.

English import Mutawarath started the day well for Waller when he recorded his third win from four Australian starts.

Another to impress was the Gai Waterhouse-trained Pureness who stretched his career record to three wins from three starts with victory in the AJC Convention Centre Handicap (1300m).

The four-year-old will now be tested in Saturday grade and is nominated for the Group One Epsom Handicap (1600m) later in the spring should he continue his winning momentum in better company.

Pureness is a half-brother to Sebring who Waterhouse trained to win the 2008 Golden Slipper and AJC Sires' Produce Stakes.

"He was never in danger today," Waterhouse said of the gelding's two length win.

"There's a restricted race for him on Saturday week and then we'll go for something more serious."

Leading jockey Nash Rawiller has been aboard Pureness in all three of his victories and believes the gelding can continue to step up as Waterhouse raises the bar.

"My main concern coming into today was that he was coming back 100 metres from his last start and I might go too slow on him," he said.

"I made it genuine from a fair way out and he did the rest.

"He's taken a while for the penny to drop, he's been winning races on raw ability and gaining experience to go along with it."