The golf world waits to see how 28-year-old Day and 22-year-old Spieth fare in backing up their fabulous 2015 seasons.
Both men won five times, with Spieth claiming two majors (Masters and US Open) to Day's maiden one (US PGA Championship).
But Day finished the season stronger as they traded the No.1 ranking, winning four of his last seven tournaments - the Canadian Open, PGA Championship, The Barclays and the BMW Championship - to finish with $US9,403,330 ($A12.89 million) in prizemoney.
He also has a good record in the Tournament of Champions, having surged home with a course record-equalling 62 last year to tie for third after being tied ninth in his other appearance in 2011.
Day and Spieth will be looking for a fast start to the year with a fit-again world No.3 Rory McIlroy expected to press his claims for a return to No.1 ahead of the first major championship showdown of the year at the Masters in April.
- AAP