The Davis Cup format is set to change next year from a year-long event to something more akin to a "World Cup of tennis," a move that was approved by the International Tennis Federation in August.
World number one Novak Djokovic has strengthened his position in the ongoing ATP finals tournaments as he defeated Alexander Zverev of Germany in the men's singles event here at the O2 Arena on Wednesday.
Cilic next will take on Novak Djokovic of Serbia, who won 6-1, 2-1 over Bosnia and Herzegovina's Damir Dzumhur who retired in the 52nd minute of the match.
Djokovic is to next square off against Croatian Marin Cilic, who defeated Grigor Dimitrov of Bulgaria 7-6 (7-5), 6-4 in the round-of-16.
Roger Federer has revealed that he has been suffering with a hand injury since the summer, but said the problem is no longer a worry as he heads into his home Swiss Open starting on Monday.
In other matches, world number 6 Marin Cilic crashed out in the second round after a 2-6, 7-6(6), 7-5 loss to Chile's Nicolas Jarry.
Luka Modric, Mario Mandžukić’, Marin Čilić and the other members of the Croatian team have already made their nation proud by being the runners-up of the 2018 FIFA World Cup.
Argentina's Guido Pella on Thursday rallied from two sets down to pull off a big upset, defeating Marin Cilic of Croatia.
All eyes on the first day will be on Roger Federer who is in the tournament eyeing record ninth Wimbledon title and continue his domination at SW19.
Eventually, Nick Kyrgios lost the semi-final match in straight sets 7-6 (7-3), 7-6 (7-4) against Croatia's Marin Cilic.
The Swiss defending champion dropped his only sets of the tournament before completing a 6-2, 6-7 (5/7), 6-3, 3-6, 6-1 win over the sixth seeded Croatian in 3hr 3min.
Win or lose Federer will remain world No.2 behind Nadal while Cilic is ensured of climbing from his current six to a career-high three.