Outstanding mare Red Tracer has narrowly beaten her heir apparent as trainer Chris Waller put an exclamation mark on a memorable Derby day with a Myer Classic quinella.

Red Tracer's win dispelled doubts about her ability over a mile as she bravely wore down her equally tenacious stablemate Catkins in the final few bounds to take out the Group One by a short half-head.

The result gave Waller a Group One double for the day at Flemington after prized colt Zoustar scored a brilliant win in the Coolmore Stud Stakes.

Red Tracer was sent out the $3.10 favourite but was forced to work overtime in the final 200m after over-racing during the run in behind the leader Catkins.

Catkins ($8), described by Waller as "the next Red Tracer", found plenty in the straight after taking up the running but Red Tracer prevailed to claim her second elite-level victory.

"It was just her usual heart that showed in the last 100 metres because it went through my mind a few times that the other horse had me beaten," Red Tracer's jockey Nash Rawiller said.

Waller was proud of both horses and while Catkins was narrowly denied, the trainer is certain her time would come.

"It's been a magic day," Waller said.

"They (Red Tracer and Catkins) are both serious horses and they've beaten the others quite convincingly.

"They both did a great job. It was a narrow margin and Catkins wasn't lying down.

"It was a very proud moment."

Red Tracer broke through for her first Group One win in the Tatt's Tiara in Brisbane early this year and Waller was confident she had more big-race wins in her.

"She's a very brave mare, she's not very big, and she deserves all the credit she gets," he said.

Catkins jockey Craig Newitt felt if the runs of the two stablemates were reversed, the result would have been different.

"I had to roll to the front and she relaxed and got her own way, but she's better having the last crack at them," Newitt said.

Fire Up Fifi ($6.50) came in 2-1/4 lengths from the Waller-trained pair in third.