Black Heart Bart has firmed to outright favouritism for the Group Two P B Lawrence Stakes at Caulfield as he bids to maintain an unbeaten record over the course and distance.

The Darren Weir-trained star is one of the headline entries for Saturday's 1400m weight-for-age race and has firmed to $3.20 with TAB fixed odds ahead of Hartnell at $3.60.

Hartnell, who has barrier nine, had opened a slight favourite when the final field market went up after acceptances on Wednesday.

Black Heart Bart, who has drawn barrier five, is unbeaten in four runs over the Caulfield 1400m, including Group One weight-for-age wins in the Memsie Stakes, C F Orr Stakes and Futurity Stakes last season.

His only defeat in six Caulfield starts was a second to Winx in last year's Caulfield Stakes (2000m).

Hartnell has never raced at Caulfield but familiarised himself with the circuit in a solo gallop on the course proper on Tuesday morning.

The gelding has finished second to Winx over 1400m at weight-for-age in his past two first-up runs in Sydney and this time dodges the champion mare who resumes in Saturday's Warwick Stakes at Randwick.

"He hadn't raced at Caulfield so we took him there for a gallop on Tuesday and all the reports were good," Hartnell's trainer James Cummings said.

"He handled the track well and enjoyed it.

"It was also good to give him a little float trip to take him out of his comfort zone. I'm looking forward to him running well on Saturday and to seeing him on dry tracks for the spring."

Craig Williams will ride Hartnell for the first time on Saturday.

Weir has six of the 14 acceptors for the Lawrence with three at single figure odds.

Tosen Stardom and Australian Cup winner Humidor are at $9.

The only other horse at single figures is the world's former highest ranked sprinter Lankan Rupee at $6 but his trainer Mick Price said on Wednesday the gelding would head to Adelaide to run in the Group Three Spring Stakes over the shorter 1200m.