McEwen, who won gold and silver in the team and individual eventing contests at Tokyo 2020, respectively, recorded a dressage score of 23.4 to finish in the lead.

The day-defining score the pair received was a 10 for the extended canter.

"It’s a shame we didn’t do that test in Tokyo," McEwen said after the performance.

"Compared to our Olympic test it was pretty much mistake-free.

"The changes were nice and clean - he can do more expressive ones but they were perfect for here, the half-passes were lovely, he was really smooth through his body and in a great rhythm.

"You can’t ask for much more than that really."

Britain’s European team champion Kitty King produced a personal best with horse Vendredi Biats to move into second, just 1.4 points behind the leader.

Compatriot Mollie Summerland and Charly Van Ter Heiden trail in third by just 0.1.

The United States' Tamra Smith on Mai Baum follows, as British duo Oliver Townend and Piggy March are level in fifth after their rides with Swallow Springs and Vanir Kamira.

Smith concluded the day on 25.3 while Townend and the defending champion recorded 25.7.

Reigning European champion JL Dublin delivered for British rider Nicola Wilson in his Badminton Horse Trials debut with a score of 26.6 - good enough for ninth.

The competition is due to continue with more dressage taking centre stage.