Rachel Alexandra has confirmed her standing as one of racing's superstars with a brilliant victory in the Grade One Haskell Invitational at Monmouth Park.Rachel Alexandra was not bothered a bit by the sloppy track in Sunday's $US1.25 million ($A1.5 million) and easily beat Belmont Stakes winner Summer Bird by six lengths."We haven't reached the depth of her yet," co-owner Jess Jackson said."She is just running to beat the competition and I don't know if she will ever get to Secretariat's records

Rachel Alexandra has confirmed her standing as one of racing's superstars with a brilliant victory in the Grade One Haskell Invitational at Monmouth Park.

Rachel Alexandra was not bothered a bit by the sloppy track in Sunday's $US1.25 million ($A1.5 million) and easily beat Belmont Stakes winner Summer Bird by six lengths.

"We haven't reached the depth of her yet," co-owner Jess Jackson said.

"She is just running to beat the competition and I don't know if she will ever get to Secretariat's records."

At this rate, who knows what Rachel Alexandra is capable of.

"She's just a tremendous filly, and I'm glad she put on a good show," winning trainer Steve Asmussen said.

"She's very special. She's been able to separate herself from everyone else."

Rachel Alexandra, the 1-2 favorite, joins Serena's Song as the only fillies to win the Haskell.

The daughter of Medaglia d'Oro became the first filly in 85 years to win the Preakness when she beat Kentucky Derby winner Mine That Bird by one length.

Jackson bought Rachel Alexandra after she won the Kentucky Oaks in May and said he wanted to run her against the boys.

Now that she's beaten them twice, Jackson just may have the best filly - ever.

"There's not been a filly as good since Ruffian," Jackson said, "and she just might be as good."

Hall of Famer Ruffian won 10 of 11 races in 1974-75, but suffered a broken leg in her famous match race with Foolish Pleasure in 1975, and was later euthanased.

Rachel Alexandra has won 10 of 13 races and $US2,498,354 ($A2.99 million), cementing her claims for the Horse of the Year title.

Asked if Rachel was the best in the land, Asmussen said: "What she can do is take care of it on the racetrack. The rest is public opinion."