BRITISH Olympian William Fox-Pitt and world number one Andrew Nicholson will tomorrow crank up their bid to land the richest prize in eventing.

Both riders are well-placed after day one of dressage at the Mitsubishi Motors Badminton Horse Trials, with Fox-Pitt lying equal fourth on Oslo alongside Ireland's Aoife Clark (Master Crusoe), and Marlborough-based New Zealander Nicholson third aboard Avebury.

Fox-Pitt and Nicholson will return to the dressage arena tomorrow afternoon on their respective principal challengers Parklane Hawk and Nereo, although several powerful combinations are queueing up to potentially dash their Rolex Grand Slam hopes.

Australian Christopher Burton currently leads the field, but tomorrow's starters include the reigning Olympic, world and European champion Michael Jung on his wonder horse La Biosthetique-Sam. Jung is currently sixth on Leopin FST.

And three of Fox-Pitt's London 2012 silver medal-winning British collleagues - Zara Phillips, Mary King and Tina Cook - are also among the Saturday line-up.

The £230,000 Grand Slam has only been won once before - by Britain's Pippa Funnell 10 years ago. It is awarded to any rider who wins consecutive Burghley, Kentucky and Badminton titles.

Fox-Pitt's Grand Slam bid was put on hold last season when Badminton was cancelled due to waterlogging, and Wiltshire-based Nicholson joined him in the race through winning Burghley last September and then Kentucky five days ago.

Due to Badminton's 2012 cancellation, Fox-Pitt was given the chance to go for the Grand Slam this season.

"The build-up has been exciting - it's good for the sport," he said. "The Grand Slam, as we've seen, is hard to win. Only Pippa has done it so far, and that speaks for itself."

Nicholson, who has never won Badminton, added: "I went to Kentucky last week to put myself in the mix for the Grand Slam, so here we go.

"I have two very classy horses here, very experienced, and I am expecting a big run from them both.

"Badminton is always about a lot of pressure, but all I can do is my best. It is about trying to win here, and if I win Badminton, I win the Grand Slam.

"But there are so many good horse/rider combinations here. To win it, I should think you will feel that you are on top of the world."

Phillips, The Queen's granddaughter, will ride her 2012 Olympics horse High Kingdom, and she underlined what Fox-Pitt and Nicholson had achieved through just putting themselves in with a shout of the Slam.

"To maintain your performance at the top level is difficult anyway, but to do it in three of the five competitions is unbelievable," she said.

"But everyone is going to be trying to stop them. They are going to have to put their best performances out there to try to win it."

Surrey-based Burton made an early bid to spoil the script today as the race for Badminton's £65,000 top prize began, guiding Holstein Park Leilani into the lead, with a second Australian combination - Sam Griffiths and Happy Times - second.

Burton's score of 43.0 penalties edged him in front of Griffiths (43.3), with Nicholson third on 45.0. Today's top nine finishers are separated by just 4.3 penalties.

"She is not the most extravagant of dressage horses, so I was really thrilled to get through the test as we did," said 31-year-year-old Burton, who was the first rider at London 2012 to complete the tight and twisting Greenwich Park cross country course clear and inside the time, when he also rode Leilani.

Sunday's cross-country test is likely to be the pivotal phase, although reigning Badminton champion Mark Todd, who rides Ravenstar and Major Milestone this year, does not anticipate the best combinations encountering too much trouble.

"It looks like a three-star course with a few four-star fences in the middle," said the New Zealander, whose legendary career includes two Olympic individual titles and four Badminton crowns.

"For the standard of field that is here, I don't think it should cause too many problems.

"You can make a mistake anywhere - the fences are there to be jumped and you have to concentrate - but I don't think it is the most difficult four-star I have seen."