Paget became the first rider in 24 years to win Badminton and Burghley on the same horse in the same year and will now seek to complete the eventing triple crown at Kentucky.
Paget took the top prize on Clifton Promise with fellow New Zealander Andrew Nicholson second and third.
Fox-Pitt, bronze medallist at the recent European Championship, was the top home rider in fourth while Tina Cook ranked tenth.
"To win Badminton and Burghley back to back is a serious achievement," said Fox-Pitt.
"He needs to enjoy the moment. It doesn't happen for many riders but he has brought that horse on so well and I take my hat off to him."
Great Britain's Pippa Funnell in the only rider to previously win eventing's Grand Slam in 2003 - though she won Burghley and Badminton on different horses.