Djokovic picked up two awards, while Federer continues to dominate the fan favorite category.
Nishikori would lose in the final of the Vienna Open to Wimbledon finalist Kevin Anderson in but a quarter-finals defeat to Roger Federer at the Paris Masters last week and the unfortunate withdrawal from the end of year championships due to injury from Juan Martin Del Potro secured Nishikori's berth at the tour finals for the fourth time in his career.
Meanwhile, Djokovic, who has made an incredible comeback this year after an elbow injury, leads head-to-head against Federer 25-22, the last win coming at the semi-final of the Paris Masters last week.
This tournament opener is a hard match to call as although Anderson has mostly had the upper hand in this particular rivalry, it is the Austrian who has won both their meetings in 2018. "I'll play with confidence", he said.
"If they stay I think it's definitely a good choice", said the Swiss.
But Ferreira finished the race in ninth place and needed an Andre Agassi injury to get in, whereas Anderson has qualified as of right as the sixth-best player of this year.
"But there was always part of me that believed I could make it back and I never thought it was impossible".
Novak Djokovic returned to No. 1 on Monday after a two-year absence and is assured of becoming the first man in the history of the ATP rankings to finish a season at the top spot after being outside the top 20 during that season. Isner has been drawn in the same group as Novak Djokovic, Alexander Zverev and Marin Cilic, with the top two playing off against the top seeds from the second group for ultimate honours. This is the third year running that eight different countries have been represented in the singles field.
The 31-year-old faces John Isner, who is ranked tenth in the world.
He has been slotted with his Wimbledon tormentor Kevin Anderson in the group stage.
"Being (ranked) number one is probably the ultimate challenge in our sport and the pinnacle of the season", Djokovic, voted by his fellow professionals as the Comeback Player of the Year, told reporters. Recent form just about gives Thiem the edge and his return game could be key in breaking down his South African opponent's chief weapon.