Burghley Horse Trials - day 4: Nicholson victorious - video
Nicholson guided the 14-year-old British-owned Avebury to glory, claiming a £62,000 top prize and securing an unprecedented Burghley treble on the same horse.
And the world number two revealed he had piled pressure on himself to secure a fifth Burghley crown of his career following what he described as “a very bad year.”
The combination’s final score of 48.1 penalties after collecting just two showjumping time faults left them well clear of runner-up and Nicholson’s fellow New Zealander Jonathan Paget aboard Clifton Promise, who was disqualified from Burghley 12 months ago.
On that occasion, Clifton Promise topped the leaderboard but then tested positive for the banned substance reserpine - a sedative - and Nicholson was promoted from runner-up.
Australian Sam Griffiths - this year’s Mitsubishi Motors Badminton champion - finished third aboard Happy Times, just ahead of Britain’s world number one William Fox-Pitt and Bay My Hero.
Yorkshireman Oliver Townend, though, saw his hopes of a second Burghley title in five years disappear after four fences down on Armada dropped him from third to eighth.
“It is an amazing feeling,” Nicholson, 53, said.
“But it is such a team effort. When you have a horse that wins something like this three years in a row, it’s not just me. I have got the luxury to be able to ride him.
“It’s three phases (dressage, cross-country and showjumping), and I know he is good in all three. I have got to do my job, and he will do his.
“It’s a special moment for me after what has been a very bad year.
“I threw away Badminton, where I shouldn’t have fallen off my horse Nereo. I felt he had a real chance of winning there.
“And at the World Games the other day, I was ninth when I wanted to get a medal, so I put a lot of pressure on myself to win here to dig me out of the doldrums a bit.”
For Avebury’s owners Mark and Rosemary Barlow, who are based in Buckinghamshire and have been long-time fundraisers for British eventing teams, it was also a red-letter day.
“To win three in a row is absolutely amazing,” Rosemary Barlow told Press Association Sport.
“Andrew is a fantastic jockey on an amazing horse. This year, Avebury also won Barbury for the third year in a row and the British Open at Gatcombe.
“The horse is a character, and everyone just loves him.”
Paget also had cause to celebrate, securing a £45,000 runners-up purse in his first four-star event since a Federation Equestre Internationale tribunal cleared him of any wrong-doing over the reserpine saga.
The 30-year-old and his legal team successfully proved the positive test was caused by a contaminated feed supplement and that he could not be blamed, although the Burghley disqualification still stood because reserpine was present during Clifton Promise’s test.
The horse’s owner Frances Stead, a former managing director of L’Oreal in New Zealand, funded the legal fight.
“It has been like hell,” she said. “It has been a very tough period.
“The fact it dragged on so long I think was inappropriate and unfair and didn’t need to happen. I think it could have been handled in a much better way from a time-frame point of view.
“And the degree to which you have to go to prove what you didn’t do is extremely hard.
“I fully funded it. It has cost a hell of a lot - well, well up into the tens of thousands.
“We stepped in to fund it because we’ve got two fabulous guys (Paget’s fellow Clifton rider Kevin McNab was also cleared after reserpine was found in his ride Clifton Pinot after Burghley last year) who are incredibly talented, work their backsides off and did not deserve the stigma and reality of a two-year ban.”
Griffiths, meanwhile, saw his hopes of the Rolex Grand Slam disappear - the bumper pay-day is awarded to any rider who wins consecutive Badminton, Burghley and Kentucky titles - but was delighted to secure another podium finish.
Griffiths did add to his £34,000 Burghley prize money with another £21,500 for finishing second in the FEI Classics Series, which rewards cumulative performances across eventing’s six annual four-star competitions.
Fox-Pitt was the overall £25,000 winner for a fourth time in his career, with Townend third.