Delaveau backed up his opening night victory in an against-the-clock competition with a second success on Lacrimoso 3 HDC a day later in the evening's main event.
The world number 47 had also come second in the Longines Speed Challenge with Ornella Mail HDC.
The rider from Normandy beat Germany's Marcus Ehning with Cornado NRW by almost two seconds, with Australian Edwina Tops-Alexander, riding Guccio, in third.
Ireland's Denis Lynch with All Star, grabbed fourth, like the top three with double clear rounds.
"It is a super show, thanks to the quality of the organisation as well as the prize money ($1 million). And so far, everything is fine for me, I am really happy," said Delaveau, a cornerstone of the French team for the last 25 years.
Well known for the subtlety of his riding and his technical skills, the 49-year-old has already won classes at the biggest shows of the planet.
He was a team medallist at the World Championships in Aachen (third in 1986), then in Lexington (second in 2010) and only one individual medal is missing from his CV - he will try to secure that at the European Championships in Herning, Denmark this summer or at the World Equestrian Games scheduled for next year on his home ground in Normandy.