Group One-winning jockey Kathy O'Hara has been on better horses, but the veteran grey Zaratone is still her favourite.

Now a 10-year-old, the Bjorn Baker-trained gelding will aim to match it with a field containing 10 Group One winners in the Group Two Warwick Stakes at Randwick on Saturday.

O'Hara has been aboard Zaratone in 23 of his 69 starts for three wins, including success at Group Three and Listed class.

While Zaratone is yet to win at the trip or class, O'Hara said toughness was on his side.

"It's a full field and obviously he's a quick horse," O'Hara said.

"He's never won at 1400 metres before, but he's such a tough old campaigner I couldn't completely rule him out."

The speedster led in his last start, the Group Two Missile Stakes, only to be swamped late, finishing 1-1/4 lengths fourth in the race won by by stablemate Burbero.

Few people know the horse better than O'Hara, who says the veteran is as keen as ever to compete.

"He loves his racing, he loves his job," O'Hara said.

"He's an old marvel.

"He's won 17 races and he's going as good as ever."

O'Hara was the first female jockey to win a Sydney Group One when she partnered Ofcourseican in the 2012 Coolmore Classic.

But despite being on board horses who have performed at the top level, the son of Zariz still holds a special place in her heart.

"He's probably my favourite racehorse - no horse tries harder than he does," O'Hara said.