Top trainer Chris Waller described jockey Jim Cassidy as a marvel after they combined to win the $125,000 Group Three Grand Prix at Doomben on Saturday.

Waller and Cassidy completed a feature race double when Hawkspur, the $3.80 favourite, beat Rhythm To Spare ($6) by 2-1/4 lengths with a short neck to Honorius ($12) in third place.

The pair had earlier combined to win the Group Two BRC Sires' Produce Stakes (1350m) with Zoustar.

Waller paid the ultimate tribute to Cassidy after the veteran rider again gave his younger rivals a masterclass in the Grand Prix.

"If Jimmy rides Hawkspur like that in the Derby he will win it," Waller said.

"Jim has ridden Hawkspur perfectly at his last two starts and he has won both.

Waller said Hawkspur had improved sharply since coming to Brisbane.

"He is a horse we set for the winter and he has come up to the mark," Waller said.

Cassidy was more blunt about Hawkspur's chances in the Queensland Derby on June 8.

"He will win. They won't beat him," he said.

Hawkspur will clash with the runner-up again in the Queensland Derby.

Glen Boss, who rode Rhythm to Spare, said his mount had run a nice race and would be fitter for the effort.

"He will eat the 2400 metres and I reckon he can turn the tables in the Derby," he said.

Michael Rodd said his mount Honorius should alo be suited in the Derby.

Filly Dear Demi did her Queensland Oaks chances next Saturday no harm when she ran on to finish sixth.

Dear Demi had come from near last at the 600m.