Richard Gasquet was the man who could have ruined the party for Ferrer or Nishikori by winning the Swiss Indoor Basel, but the Frenchman was knocked out in semi-finals.
As a result, Nishikori and Ferrer will join Novak Djokovic, Andy Murray, Roger Federer, Stan Wawrinka, Tomas Berdych and Rafael Nadal in London from 15-22 November.
Nishikori will be making his second appearance at the event while Ferrer will be turning out at the tournament finale for the seventh time.
“I am very excited to go back to London,” Nishikori told the official ATP website. “Being part of the best eight players in the world is a big honour and something I work very hard for every day. This tournament is one of the flagship tournaments of the year for us and I look forward to coming back.”
Ferrer said of his qualification: "It’s an honour to be back in London and be amongst the best players in the world once again. It’s been a great season for me and I really look forward to the tournament."
Final ATP Tour Race to London standings:
Novak Djokovic - 14,285 points
Andy Murray - 7,870 points
Roger Federer - 7,250 points
Stan Wawrinka - 6,140 points
Rafael Nadal - 4,450 points
Tomas Berdych - 4,440 points
David Ferrer - 3,945 points
Kei Nishikori - 3,945 points