Great Britain's Olympic hopefuls stayed in touch with the leaders after the first round of the dressage on day one of the Badminton Horse Trials.

Australian Clayton Fredericks and Nullabor scored high marks to lead at the half-way point in the dressage.

British Olympic hopeful William Fox-Pitt is fifth on Ballincoola, with world eventing champion Zara Phillips and her first ride, Glenbuck, sixth.

GB selectors will finalise the Olympic equestrian team after Badminton.

Given the wet weather affecting the opening day of the three-day competition, Fredericks was pleased with his performance.

"In the conditions I am very happy to be where I am," said Fredericks, who is based in Britain.

"Nullabor is now much more confirmed at the level and really lets me ride him."

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Mary King, who, like Phillips, is regarded as a certainty to represent Britain in Beijing, finished 14th on Apache Sauce.

Phillips rides again on Friday with Ardfield Magic, while King partners Imperial Cavalier. Fox-Pitt has left his main Games hope, Parkmore Ed, at home.

Veteran Pippa Funnell is also aiming to win a place in the British team and the 39-year-old begins her quest on Friday with Ensign.

Phillips said of her ride, Glenbuck: "He has loads of scope. It's just trying to get him to settle because he is so strong."