Here are the profiles of the singles players who will be taking part.
Thiem, on the other hand, has the unique mixture of experience and youth.
In terms of a contest, nothing works better than the Federer-Djokovic duel. The indoor hard-courts, with their controlled environment, provide an nearly ideal canvas for Federer's artistry. Each has beaten the other at all the four Majors.
That's preceded by the opening doubles match, in which another South African qualifier, the Wimbledon doubles runner-up Raven Klaasen, competes at the ATP Finals for the second time.
But it is hard to see anybody other than Federer or Djokovic prevailing.
Amnesty International had urged Nadal and Djokovic not to play. With Rafael Nadal out of the mix this year, Djokovic and Federer are the players to beat and Thiem could be just the player to make an impact. Federer hasn't quite played well this season and has scraped past many an opponent, but he has reasons to be optimistic.
Saints’ Dez Bryant hurt, calls injury the ‘ultimate test’
When the New Orleans Saints agreed to terms with free agent wide receiver Dez Bryant , the earth felt like it was moving. Per Schefter, the Saints could turn to Brandon Marshall , who also worked out for the team along with Bryant recently.
'I think if they stay it's definitely a good choice, ' said Federer.
'I feel like he's very quickly played a top 30 level, ' said Federer of what he saw from Murray this summer. It's better than it was in Basel. "I don't have much to lose, so I'll play loose and free". This will be whittled down next month to a shortlist of about five and a final decision on the host of... His rise to the No. 1 spot, after being outside the top 20 as recently as in July, has been meteoric.
"It turned to out to be a ideal five months of the year, with two Grand Slam titles", he added. Can he pick up the biggest title of his year at the ATP Finals in London? While Anderson had a breakthrough last season, making it to the US Open finals, the 33-year-old Isner has taken a little longer. At Cincinnati, Federer hadn't lost in seven final appearances and hadn't suffered a service break since 2013.
Marian Vajda was the favourite when the ATP Coach of the Year nominees were revealed, and expectations were fulfilled.
Does all this mean that the other six men in the fray at the Finals will be reduced to supporting actors or is there a pleasant surprise in store like Grigor Dimitrov's triumph past year?
After then enjoying the hospitality of Her Majesty's government in a setting as far removed from ordinariness as it is possible to get, they return to their day jobs on Sunday, Federer lighting up the evening programme against Kei Nishikori. In fact, the trio of Cilic, Zverev and Thiem collectively won two matches out of nine at the 2017 Finals and crashed out in the round-robin stage.
The 19-year-old is all but guaranteed an Australian Open seeding after last year winning his way into the tournament through the wildcard playoff. "We've always been proud of our ability to bring some of the world's best talent to New Zealand, and having players go on and qualify for the Finals just emphasises that" said Budge. Check back to see if the rising star can knock out some of the sport's greatest players. "I think the options clearly are also important to look at".