All of the qualities trainer John Thompson looks for in a top-class filly can be found in Coolmore Classic favourite First Seal.

"She's big, she's strong, she's a good doer, she's a good worker, all of those things," Thompson said.

But sometimes the superior talent can come with some baggage.

Even the best racemares like dual Coolmore winner Sunline can have a nasty streak and some trainers swear that without that trait they might not have made it to the top.

With First Seal there is no attitude - at least not anymore. In her trainer's eyes she is a darling.

"She has a lovely nature," Thompson said.

"She was a bit stubborn early on but this preparation she has turned the corner."

The three-year-old completely dominates betting on Saturday's Group One race at Rosehill and at $1.70 is the only one of the 13 runners under double-figure odds.

Yet in the back of Thompson's mind is the reality that First Seal still has to prove herself against older, more seasoned horses.

She also has to do it with 55.5kg and from a wide barrier.

He says those factors add to her task in a race that will determine whether Thompson sets her on a Doncaster Mile path.

"It's more of a challenge and it's an unknown thing going up against the mares," Thompson said.

"The barrier makes it a little bit harder again but I think she's better drawn a bit wide and getting plenty of room, rather than draw inside and get cluttered up."

First Seal was an easy last-start winner of the Surround Stakes, the same lead-up race used by six of the past seven three-year-olds to have won the Coolmore.

Thompson says her trackwork since has been that of a horse who will be even better at her third campaign run.

"She had her main gallop on Saturday and (jockey) Blake (Shinn) got off her and said she just keeps making those little improvements," Thompson said.

"Hugh (Bowman) galloped her on Tuesday because Blake wasn't here and when he got off his words were `she feels awesome'.

"Hughie doesn't say much so I was happy with that."

Plucky Belle, which at six years of age is the oldest runner in the Coolmore, is regarded as First Seal's biggest threat at $11.

Thump is $12 to give Kris Lees his first victory in a race his late father Max won five times.

HISTORY OF THE COOLMORE CLASSIC

* Sunline is the only horse to win the race twice in 2000 and 2002, carrying maximum topweight of 60kg each time

* Seven fillies have won in the past 20 years - Kapchat (1994), Assertive Lass (1997), Bollinger (2003), Shamekha (2004), Regal Cheer (2006), Tuesday Joy (2007), Typhoon Tracy (2009)

* Max Lees' five winners were Satin Sand (1986), Quicksilver Cindy (1991), Flitter (1995), Chlorophyll (1996) and Shindig (1998).