Jockey Steven King is happy to back the judgment of trainer Danny O'Brien who has engaged him for AJC Australian Derby flop Buffett in the VRC St Leger Stakes at Flemington.

King is having his first ride on the three-year-old and is trying to win the St Leger (2800m) for the first time on Saturday.

O'Brien has three runners in the Listed feature and has booked Steven Arnold for Pentire Point and Stephen Baster for Bellabaci.

A Geelong winner and placed three times from nine starts, Buffett is the best performed of the trio and is coming off a last-start 10th to Roman Emperor in the Derby on April 11.

A week earlier he finished a close fourth to Derby runner-up Harris Tweed in the Group Two Tulloch Stakes (2000m) at Rosehill.

"This is my first time on the horse but Danny has kept him going after the Derby failure so you have to be taking a positive from that," King said.

"Take his Derby run away and you would think he would be hard to beat."

King has had a successful association with O'Brien in the past with horses such as dual Group One winner Glamour Puss.

He said Buffett had drawn well in barrier two to get a perfect run in a field of 11 filled with hopeful stayers rather than proven, class three-year-olds.

The David Hayes-trained Berlioz, who last start finished second to Markus Maximus in the WA Derby (2400m), is considered the hardest for Buffett to beat.

TAB Sportsbet has only just managed to split the pair with Berlioz at $3.40 and Buffett at $3.30.

Bellabaci is $6.50 while O'Brien's other runner Pentire Point is $10.

The St Leger is a qualifying race for the Melbourne Cup and 14 horses have won both races, the last Gurner's Lane in 1982.

In 1991 St Leger winner Shiva's Revenge finished second in the Melbourne Cup while 1995 winner Count Chivas ran in four Melbourne Cups, including his second to Saintly in 1996.

Another St Leger winner, Dolphin Jo (2006), has run in two Melbourne Cups and finished fifth to Efficient in 2007.

King is also hoping to revive the fortunes of Playwright who was another Sydney failure and is lining up in Saturday's Listed Auckland Racing Club Handicap (1610m).

Playwright loves his home track at Flemington and finished second to Largo Lad in the Group Two Blamey Stakes (1600m) three starts ago.

In Sydney he produced two unflattering runs, finishing seventh in the Group Two Ajax Stakes (1500m) and 11th at Randwick over 1600m on April 11.

"Coming back here with no weight he is entitled to bounce back to his Largo Lad form," King said.