That doesn't guarantee Olympic selection; merely that the combination is entitled to be chosen in the New Zealand squad, if the selectors deem it good enough.
A group of five combinations - a team of four and one individual rider - will be named next year. The final qualifying event is at Barbary Castle in Wiltshire from June 28 to July 1.
Nicholson, with three horses entered, heads a New Zealand contingent to the four-star Les Etoiles de Pau event this weekend.
It is the final leg in the FEI Classics series, eventing's grand slam, and also the first event of the 2011-12 season.
Todd is sitting fourth on the classics leaderboard but is not competing at Pau, however Nicholson is sixth, Caroline Powell seventh and Jonathan Paget 15th.
The dressage stage starts tonight. The series winner pockets US$150,000, with prize-money running through to US$25,000 for fifth spot.
Britain's Mary King leads the field on 38 points, Todd has 15, Nicholson 14 and Powell 13.
The Olympics start on July 27. Combinations to have qualified for Olympic selection are: Andrew Nicholson and Nereo, Avebury, Mr Cruise Control, Armada, Shady Grey; Caroline Powell and Boston Two Tip, Port Hill Rusty Nail, Lenamore; Mark Todd and NZB Campino, Major Milestone; Jonathan Paget and Clifton Promise, Clifton Lush; Clarke Johnstone and Orient Express, KS Secrets; Lucy Jackson and Kilcoltrim Ambassador; Jonelle Richards and Flintstar; Neil Spratt and Upleadon.