FRENCHMAN Thibaut Vallette upstaged Olympic champion and world number one Michael Jung for a second time in nine months as he took an overnight lead at the Mitsubishi Motors Badminton Horse Trials today.

German star Jung, the Badminton title holder, will need to come from behind in his pursuit of a record £100,000 top prize.

Vallette was part of the French quartet that defeated Jung and company for team gold at last summer's Rio Olympics, and he now leads Badminton on Qing du Briot after posting a dressage score of 38.7 penalties.

Germany's Bettina Hoy and Designer 10 are second, with Jung's 40.0 penalties aboard La Biosthetique Sam leaving him third, just ahead of another French contender Astier Nicolas, who won silver in Rio last year while based at Stockley, near Calne, and double Olympic champion Mark Todd, who is based at Wanborough.

Badminton debutant Alexander Bragg, riding Zagreb, and Tom McEwen with Toledo de Kerser, lead the the British challenge in equal sixth spot.

Jung's dressage mark was more than five penalties worse than his Badminton performance last year, but even if he has left the door slightly ajar, he had no intention of showing it.

"You hope always the test is better, but in the end, I think it was a good test with a few little mistakes," Jung said.

"There is a lot of pressure here. We had a few good marks and a few not so good marks.

"I am happy my horse is full of energy. That is good for (cross-country) on Saturday, and he is brilliant at that. I am looking forward to it - conditions are perfect."

Only one French rider has won Badminton during its 68-year history - Nicolas Touzaint in 2008 - but 43-year-old Vallette has put himself on course halfway through the dressage phase, with Friday's action set to showcase major title contenders such as Ingrid Klimke, New Zealander Andrew Nicholson, who is based near Marlborough, and Britain's Gemma Tattersall.

Vallette said: "I am very happy. It was the best test the horse has done this year.

"He has had some difficulties since Rio, and although we made a few mistakes at the beginning of the test, he was then listening to me again. I didn't expect to do so well."

Marlborough-based New Zealander Jesse Campbell and Kaapachino were down in 21st, with Nicholson a further 11 places back on the other of his two horses Qwanza.

Marlborough's Lissa Green and Malin Head Clover were lying 39th.

There was disappointment, though, for highly-rated British prospect Laura Collett, who withdrew her ride Grand Manouevre before the competition started.

Lambourn-based Collett tweeted that the horse slipped on concrete just five minutes before Wednesday's first horse inspection, adding: "He was just a bit stiff this morning - we have to look after him."