Wet weather had made ground conditions tricky throughout the event, and Nicholson and nine-year-old Quimbo were 108th of the 112 strong field to go in the cross country.
"It looked worse than it rode, but the same narrow track ridden by so many gets quite deep. It becomes a lot harder work for him but he coped very well."
It is the second time Nicholson has won Boekelo.
Quimbo has been with Nicholson since he was three, and has consistently featured on the podium.
Just two weeks ago Nicholson and Quimbo won the eight and nine-year-old championship at the Blenheim Palace International Horse Trials, and inlate August, Nicholson and Avebury won the Burghley International Horse Trials.
"Now we just need to do the same at Pau," he said, of the four star event in two weeks time.
Other Kiwis to feature in the top 20 were Mark Todd and Leonidas II who were 17th, Megan Heath aboard St Daniel in 18th spot and rising young star Jesse Campbell on Kool Kaapachino who were 20th.
In the Nations Cup event at Boekelo, New Zealand couldn't do enough to slide past eventual winners Germany.
