Leading the field is US rider Allison Springer on Arthur (36.9), who rerouted to the event after being eliminiated on the cross-country at Burghley.
In second place is British rider Emily Baldwin on Drivetime, with 38.5 penalties.
Caroline Powell and Boston Two Tip (51.9) are the next best placed Kiwis after Nicholson, with Mark Todd on Grass Valley 16th on 57.7. Neil Spratt and Charlton Noted (63.3) are 25th and Craig Nicolai and Just Ironic are 27th on 64.8.
The remaining 40 riders perform their dressage tests today. They include Kiwis Joe Meyer (Sanskrit), Neil Spratt (Upleadon), and Mark Todd and Land Vision.
The dressage for the CIC*** for 8 and 9-year-olds also takes place today, with Nicholson riding Oplitas and Avebury in the event.
Results after dressage day 1
Judges: Christoph Hess GER (E), Gillian Rolton AUS (C), Tim Downes GBR (M)
ARTHUR Allison Springer GB 36.9 1
DRIVETIME Emily Baldwin GB 38.5 2
MR CRUISE CONTROL Andrew Nicholson NZ 46.2 3
MAGENTA Alex Hua Tian CHN 47.7 4
REDESIGNED Pippa Funnell GB 48.3 5
MITRAS EMINEM Dag Albert SWE 48.6 6
IGOR DE CLUIS Ibby Macpherson GB 48.8* 7
EXPLORING Jessica Phoenix CAN 49.2 8
CHAPEL AMBLE Nick Gauntlett GB 50.4 9
CHILLI MORNING Nick Gauntlett GB 50.8 10
BOSTON TWO TIP Caroline Powell NZ 51.0 11
NZB GRASS VALLEY Mark Todd NZ 159 156 165 57.7 16
CHARLTON NOTED Neil Spratt NZ 162 141 148 63.3* 25
JUST IRONIC Craig Nicolai NZ 151 145 147 64.8 27
* - denotes errors of course