The groupings for the ATP Finals were announced Monday for the year-end event which begins on Sunday.
Former champions and favorites Novak Djokovic and Roger Federer are the only players to have made the finals of the tournament before.
Year-end No. 1 Djokovic is mixed in with big men Alexander Zverev, Marin Cilic and John Isner, all of whom are at least 6-foot-6. Overall, the Serb is 25-5 against those three players.
While Federer deals with Kevin Anderson, Dominic Thiem and former semifinalist Kei Nishikori. Federer is 13-4 against his fellow Hewitt group foes.
John Isner is the lone debutant among the eight. Four players – Federer, Cilic, Nishikori and Thiem – return from last year.
Federer has won the title six times, Djokovic five, so 11 of the last 15 years the title as gone to one of those two. The 19th-ranked 2017 champion Grigor Dimitrov did not make it back to the event.
Karen Khachanov and Borna Coric will serve as the alternates. Rafael Nadal and Juan Martin del Potro were both withdrawals.
Matches begin Sunday with the Hewitt group featuring Federer-Nishikori and Thiem-Anderson. On Monday, Djokovic meets Isner and Cilic battles Zverev.
2018 ATP FINALS GROUPS
Singles – Group Guga Kuerten
 Novak Djokovic (SRB)
 Alexander Zverev (GER)
 Marin Cilic (CRO)
 John Isner (USA)
Singles – Group Lleyton Hewitt
 Roger Federer (SUI)
 Kevin Anderson (RSA)
 Dominic Thiem (AUT)
 Kei Nishikori (JPN)
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