The American rider, on board RF Scandalous, earned 21.7 points to top the scoreboard ahead of British duo Oliver Townend and William Fox-Pitt in the dressage leg of the five-star competition.

The impressive points tally was the best since 2009 when Germany's Bettina Hoy, riding Ringwood Cockatoo, scored a 19.2 and Britain's Lucinda Fredericks, on board Headley Britannia, earned a 21.5.

"It’s great to be back here in Kentucky," said Little.

"It’s a great gauge.

"The last time she was here she was on a 24.8 [after dressage].

"She’s so much more mature and we’ve both learned so much.

"Riding a horse like Scandalous here is also a privilege.

"She’s my horse of a lifetime.

"I’m acutely aware of that and trying to make sure I’m enjoying every moment with her."

Townend, riding Cooley Master Class, is attempting to defend his 2018 and 2019 Kentucky titles this week and got off to a good start, scoring a 24.1 to sit second.

"I think that’s the best test he’s done at Kentucky," said Townend.

"He’s on the same score as [2019] but it’s a different test which possibly doesn’t suit him quite as well."

Three-time Kentucky champion Fox-Pitt, competing at the event for the first time since 2015, collected 27.9 on board Oratorio to climb to third.

"It’s very nostalgic to be back here," said Fox-Pitt.

"Driving into the Park I felt quite emotional and excited.

"It’s great to feel like that."

There is a three-way tie for the lead after the first day of dressage in the short four-stae competition, with an American trio battling it out for top spot.

Tamie Smith, riding Danito, Doug Payne, on board Starr Witness, and Liz Halliday-Sharp, riding Cooley Moonshine, all received a score of 28.1.

Smith set the bar as the first to earn the leading score and she believes Danito is capable of better marks.

"He was really fresh and kind of naughty [in warm-up]," Smith said.

"I went into that test today not being able to really ride him, so I was disappointed after my ride.

"He can produce a much better test than he did today.

"He’s such a cool horse and such a trier and I really love him."

The scores are close at the top, with the best nine of the first session all scoring fewer than 32.0 penalties.

Competition is set to continue tomorrow.