New Zealander Mark Todd, returning to the Badminton horse trials in England after a 10-year absence and 30 years after his first win there, made an inauspicious start overnight (NZT).
The double Olympic champion, who has won Badminton three times, struggled on his relatively inexperienced horse Grass Valley in the dressage.
"He worked beautifully outside yesterday and I thought a good test - maybe less than 50 penalties - was possible," Todd said.
But the atmosphere in the arena, with many spectators taking seats just for Todd's test, caused some minor errors and Grass Valley's score ended up at 55.8, putting them into 23rd place after half the 83-strong field completed their tests.
The second half of the field does dressage on Saturday (UK time), with the cross-country Sunday, and the final phase, show jumping, on Monday.
Todd said he "felt like he'd never been away" in spite of the 10-year gap. "The fences are similar, but it is different without the endurance phases of roads and tracks and steeplechase. I prefer this shorter format now because I think it's better for the horses."
Best placed of the New Zealanders after the first day of dressage is Joe Meyer riding Clifton Lush in 13th place on 49.5 penalties, followed by Andrew Nicholson and Nereo on 51, in 16th.
The overnight leader on 39 is Britain's Ruth Edge with Two Thyme, five penalties ahead of compatriot Kitty King riding the New Zealand thoroughbred Boondoggle, formerly ridden by Christchurch's Tim Price.
NZPA