"It's been a great day for the sport. The weather conditions were ideal for riding cross-country, the grounds are superb and the horses just love to gallop on it."
Nicholson had promised he would be riding Quimbo like a "hardened four-star performer with a chance of winning", and did just that.
But there were still challenges aplenty for others on the Derek di Grazia-designed cross-country course. Of the 42 starters, seven were eliminated and five retired - including overnight leader William Fox-Pitt (Great Britain) aboard Chilli Morning.
The showjumping today will decide the winners, and Nicholson said he expected Quimbo to do his job, although it is a discipline that sometimes challenges Calico Joe.
Third behind Nicholson is Buck Davidson Jnr (USA) with Ballynoe Castle RM who has 45.2, with Fox-Pitt and Sea Cookie TSF on 46.2 in fourth, giving the Kiwi a rail in hand.
Nicholson is chasing not just victory at Kentucky but points in the HSBC FEI Classics, which he leads.
The Rolex Kentucky three-day Event is the Western Hemisphere's only four-star three-day event. It features the world's best horses and riders vying for their share of US$250,000 ($295,000) in prize money, as well as the chance of US$350,000 for winning Kentucky, Mitsubishi Motors Badminton and Land Rover Burghley four-star events in succession.