Riding on Graf Liberty, Burton achieved the third lowest score in Badminton history by ending on a total of 32.9 penalties.

Only fellow Australian Andrew Hoy and Britain’s Pippa Funnell have achieved better scores in the event’s 68-year history.

"I’m so proud of my horse, I can’t believe it,” said Burton.

“I deliberately didn’t push him too much at the start of the week.

“I didn’t even get on the horse until Wednesday afternoon as I have been known to overdo it on him before, but he worked in better and better and to come out of the arena with a 32.9 is fantastic.

“I’m so happy."

Germany’s Ingrid Klimke lies in second place in the standings, as she seeks to improve on a runners-up finish back in 2015.

Riding on Horseware Hale Bob, the 49-year-old is just 3.5 penalties behind the leader after the first two tests of the competition.

Ireland’s Jonty Evans, riding at the event for the first time in 10 years, and Belgium’s Karin Donckers lie in third and fourth place overall.

The pair have 37.2 and 37.3 penalties to their name.

France’s Thibaut Vallette, who led the overnight standings, has slipped to seventh place overall.

Defending champion Michael Jung will have work to do on the final two days if he is to win the title again.

Germany's three-time Olympic gold medallist is ninth, trailing by a total of 7.1 penalties.

The cross-country test is then due to take place on tomorrow, before the Badminton Horse Trials conclude with the jumping test on Sunday (May 7).

The Badminton Horse Trials are part of the International Equestrian Federation (FEI) Classics series.