Having claimed some big scalps in the Australian Guineas with Shamrocker, trainer Danny O'Brien is turning his attention to Star Witness and the challenge against Black Caviar in the Newmarket Handicap.The VRC Oaks runner-up, Shamrocker caused an upset in Saturday's Group One Guineas at Flemington beating Bullbars and Playing God.O'Brien admits it will be an even bigger upset if Star Witness can beat Black Caviar in Saturday's $1 million sprint at Flemington but he is not running and hiding from

Having claimed some big scalps in the Australian Guineas with Shamrocker, trainer Danny O'Brien is turning his attention to Star Witness and the challenge against Black Caviar in the Newmarket Handicap.

The VRC Oaks runner-up, Shamrocker caused an upset in Saturday's Group One Guineas at Flemington beating Bullbars and Playing God.

O'Brien admits it will be an even bigger upset if Star Witness can beat Black Caviar in Saturday's $1 million sprint at Flemington but he is not running and hiding from the task.

A dual Group One winner as is Black Caviar, Star Witness has run into the Peter Moody-trained four-year-old twice, finishing four lengths behind her on each occasion under weight-for-age conditions.

The Starcraft colt was fourth to her in the Group Two Schillaci Stakes (1000m) at Caulfield and runner-up in the Patinack Farm Classic (1200m) at Flemington, both last spring.

"Obviously Black Caviar is so far and above every other sprinter at the moment," O'Brien said.

"But now we've come back to sprinting, we'll run him in the Newmarket.

"He's a very, very good horse down the straight, having been beaten only once (in three starts) and that was by her."

Black Caviar, the Newmarket topweight with 58kg, will be giving away a five kilogram advantage to Star Witness.

The three-year-old meets Black Caviar marginally better than the 3.5kg and 3kg he got off her in the Schillaci and the Patinack Farm Classic respectively.

"I'm certainly not going to the races thinking we are going to beat her but we'll be turning up and giving ourselves a chance," O'Brien said.

"She was every bit as impressive winning the Lightning as what she was in winning the Patinack Farm Classic.

"We had a close look at her with Star Witness in the Patinack and she ran away from him like he wasn't there and she did the same thing to Hay List in the Lightning.

"I've never seen a horse do what she can do."

Star Witness was beaten first-up as odds-on favourite when he finished third to Enjin Number Nine in the Manfred Stakes (1300m) at Sandown on February 9 after which O'Brien backed away from running him in the Australian Guineas.

"It was a very biased track that day and he just couldn't get into the right lane (from barrier one)," O'Brien said."

"We hadn't seen him past 1200 metres before. We think the 1300 is as far as he wants to go and we're pleased to come back to what he does best and that's as an explosive sprinter."

Star Witness was scratched from the Oakleigh Plate (1100m) at Caulfield last Saturday week due to an elevated temperature on race morning.

O'Brien said Star Witness would go to England for the Royal Ascot meeting if his form warranted it.

"It will depend on his next couple of runs. Obviously we want to see him produce the form he showed in the spring (when he won the Coolmore Classic)," he said.

"If he can turn up and run second (to Black Caviar) in the Newmarket, it's definitely not going to be any embarrassment.

"I think he's particularly well suited in a race like the King's Stand Stakes at Royal Ascot.

"If he shows he's in the form he was in the spring then that's the way he'll be heading."

Star Witness, who won the Blue Diamond Stakes in his two-year-old season, will be retired to stand at Widden Stud in the Hunter Valley this spring.