The Nitto ATP Finals groups are set—including late addition John Isner

Stories of the Open Era: ATP Finals

The Paris Masters helped finalized the field for the eight-player Nitto ATP Finals, the season-ending, round-robin tour showcase held at London's O2 Arena. But while Marin Cilic and Dominic Thiem clinched spots in the exclusive tournament with Top 8 finishes in the ATP's Race to London, Kei Nishikori and John Isner secured passage through other, unfortunate circumstances: the injury-induced withdrawals of Juan Martin del Potro (world No. 4; 5,300 ranking points) and Rafael Nadal (world No. 2; 7,480 ranking points).

It's a bit of good fortune for Nishikori and Isner, of course, with the American set to play in his first year-end championship after narrowly missing out a year ago. It's the fourth time Nishikori will compete in London.

With the participants confirmed, the groups were drawn on Monday:

Both groups will include a first-time participant—Kevin Anderson is the other debutant—and a former champion: Novak Djokovic has won this event five times; Roger Federer has won it a record six times. It's also the first time Federer and Djokovic have both played the event since 2015, when the Serb topped the Swiss in the final for his most recent title.