AMERICAN Clark Montgomery delivered a sparkling dressage performance to lead the Mitsubishi Motors Badminton Horse Trials heading into Saturday's critical cross-country phase.

Montgomery posted a score of 33.3 penalties aboard Loughan Glen to move ahead of long-time leader and 2010 Badminton champion Paul Tapner, the AUstralian based near Highworth.

"He felt amazing," said 32-year-old Montgomery, who would become the first American winner of Badminton since David O'Connor 17 years ago if he triumphs this weekend.

"I knew he could do it, and it was just a case of whether he was going to give it me or not."

Sussex-based Francis Whittington, who was among Thursday's dressage starters, remains the highest-placed British rider in third spot, but a veritable who's who of eventing have formed a queue behind him.

British star and world number one William Fox-Pitt is equal-seventh aboard his previous four-star winner Parklane Hawk, while New Zealand's former double Olympic individual champion Mark Todd, based at Badgerstown near Marlborough, has two horses - NZB Campino and Leonidas II - in the top 10.

Todd's fellow New Zealander Andrew Nicholson, based near Marlborough and the rider Fox-Pitt recently replaced as world rankings leader, posted the same dressage score of 41.0 as his fierce British rival on Nereo.

And Sweden's Sara Algotsson Ostholt, who was pipped to individual gold at London 2012 by German Michael Jung, is on 40.5 with Reality 39, suggesting a thrilling day's cross-country action lies ahead across the Badminton parkland.

Weather conditions are forecast to be poor, which points to soft going and a stamina-sapping challenge, especially for the later starters.

Organisers on Friday removed part of a potentially-troublesome logs complex at 18, a three-part challenge that had been questioned by many riders on early inspection of the course.

"I hate fence 18 with a passion! I am not sure that he (course designer Guiseppe Della Chiesa) has got that right," Olympic medallist and 2009 European individual champion Tina Cook said, before the change was made.

But Cook, 23rd overnight with De Novo News, added: "I think the course is super.

"My complaint has been that over the last few years it's lacked variety, and Guiseppe has added that.

"It is bigger and wider, very much a Badminton course. Badminton is always a step up from everything else, but this year it's a massive step up from three-star level.

"They've done everything they can with the ground, and it's got great grass cover. You've got to be brave and bold and keep pushing, and it is those riders that will do well."