Dwayne Dunn believes Ortensia only needs to bring her best to Flemington on Saturday to add another straight track Group One to her record in the Newmarket Handicap.

Dunn has never ridden Ortensia but is thrilled to have picked up the ride in the famous 1200m sprint with Craig Williams to partner three-year-old Better Than Ready.

The Paul Messara-trained Ortensia won a Listed race down the straight at Flemington during the 2011 spring carnival and has also been successful in the Group One Al Quoz Sprint in Dubai and the Group One Nunthorpe Stakes in England on straight courses.

"If she brings her `A-game' she should be beating them," Dunn said.

"But there's a lot of horses in there going well. I'm as confident as I can be that she'll perform to her best. And if she does that she's going to be very hard to beat."

Ortensia's Newmarket weight of 56.5kg was considered attractive by Messara and Dunn said his main focus would be getting the classy sprinter into clear running on the outside so she has the time to power home.

He isn't concerned about not riding the mare ahead of the Newmarket.

The seven-year-old finished 11th in the Oakleigh Plate in her first start since September and will jump from barrier nine in the 14-horse Newmarket field.

"I think half the trick is getting her into clean air and getting her balanced," Dunn said.

"When she gets that she can reel off really good sectionals."

Ortensia is on the fifth line of betting at $13 with Moment Of Change a clear favourite.

Moment Of Change stamped his Newmarket credentials with his second to champion stablemate Black Caviar in the Lightning Stakes.

Seven of the past eight Newmarket winners have come through the Lightning.

Unbeaten Perth sprinter Barakey missed a crucial first-up run in the Oakleigh Plate when he was scratched at the barriers but is on the second line of betting at $5 ahead of Better Than Ready ($5.50) and Luckygray ($7.50).

Ortensia forms part of a strong book of Saturday rides for Dunn who also partners last-start winner Foreteller in the Australian Cup.

He also has three rides for Anthony Cummings including the promising filly She's A Fox.