World number three Roger Federer must beat South Africa's Kevin Anderson in his last group match to make the semi-finals.
Roger Federer is now in danger of failing to qualify for the semi-finals for just the second time in 16 appearances at ATP Finals.
Roger Federer and Novak Djokovic, along with six fellow tennis stars travelled to Westminster by the London Underground.
Defending champion Rafael Nadal downed battling ninth seed Dominic Thiem 0-6, 6-4, 7-5, 6-7 (4/7), 7-6 (7/5) to reach the semi-finals for the seventh time.
Defending champion confrontation to defeat battling ninth seed Dominic Thiem 0-6, 6-4, 7-5, 6-7 (4/7), 7-6 (7/5) and reach the semi-finals for the seventh time.
Defending champion Rafael Nadal on Sunday reached the US Open quarter-finals for the eighth time where he will face Dominic Thiem, one of only three men to defeat him in 2018.
The 24-year-old Austrian was playing in his first Grand Slam final, and although he pushed Nadal at times, he fell to an ultimately one-sided 6-4, 6-3, 6-2 defeat.
Rafael Nadal joins Australia's Margaret Court as the only player to win 11 titles at the same major.
Rafael Nadal outplayed Dominic Thiem 6-4, 6-3, 6-2 to clinch his 11th French Open title.
Nadal, with 16 majors to his name, will play his 24th Grand Slam final at Roland Garros against Dominic Thiem who is in his first.
Dominic Thiem is the only man to beat Rafael Nadal on clay in the last two seasons - in Madrid this year and Rome in 2017.
Seventh seed Thiem is the first Austrian to make a final at the majors since Thomas Muster was champion in Paris in 1995.
Marco Cecchinato, who had never won a Grand Slam match in his career before the French Open 2018, will face Dominic Thiem for a place in Sunday's final.
Dominic Thiem on Tuesday cruised into the semi-finals of the French Open defeating Alexander Zverev in straight sets.
Highly-rated Canadian teenager Denis Shapovalov was knocked out by Germany's Maximilian Marterer 5-7, 7-6 (7/4), 7-5, 6-4.
Alexander Zverev has long been marked out as a future star of the men's game and his victory suggests the German can be a major threat at the French Open later this month.
The shock result on Friday also means that Roger Federer will reclaim the world number one ranking on Monday
The Spaniard is now just two wins away from a record 31st Masters title, after winning 32 consecutive sets on clay.