A dramatic day at the Association of Tennis Professionals (ATP) Finals saw Dominic Thiem beat Rafael Nadal in two tie-break sets before defending champion Stefanos Tsitsipas beat Andrey Rublev in a deciding set tie-breaker.
The top eight players in the ATP singles and doubles rankings are participating in the competition, which is now on its third day of competition.
Action is taking place in a round-robin format to determine the semi-finalists and today saw the second round-robin matches in Group London 2020.
The first singles match of the day saw the winners from the first round of group matches go head-to-head as second seed Dominic Thiem of Austria beat third seed Rafael Nadal of Spain 7-6 7-6 in a match lasting two hours and 25 minutes.
The first set tie-break looked like it was heading Nadal's way at five points to two in the Spaniard's favour but Thiem increased his aggression and saved two set points before clinching it by nine points to seven in 72 minutes.
In set two, the first break of the match came at 3-3 and went to Nadal.
Thiem responded immediately to break back and had a chance to close the match out when he had three break points on Nadal's serve at 5-5.
The Spaniard saved them and forced another tie-break which was level at three points apiece before Thiem won three straight points and closed the tie-break out by seven points to four.
Thiem's qualification was secured when defending champion Stefanos Tsitsipas of Greece, the sixth seed, defeated Andrey Rublev of Russia, the seventh seed 6-1 4-6 7-6 in a topsy-turvy encounter at The 02 Arena.
Tsitsipas cruised to the first set in just 20 minutes 6-1 as the Greek player dominated with his serve against an out-of-sorts Rublev.
In the second set the Russian reduced his error count and increased his aggression and in the tenth game he broke Tsitsipas' serve to take the set 6-4.
The third set was an even contest that went all the way to a tie-break and at 5-2 it appeared as though Tsitsipas was on course for victory.
Rublev battled back to earn a match point but could not convert it as he served a double fault.
Tsitsipas made the most of the reprieve and closed the tie-break out by eight points to six, with his win sending Thiem through to the last four while also eliminating Rublev's chances of progressing from the group.
Tomorrow's singles matches see the second round of games in Group Tokyo 1970 take place.
The day session match, scheduled to start at 2pm BST sees the two defeated players from the first round of games, Alex Zverev of Germany, the fifth seed, and Diego Schwartzman of Argentina, the eighth seed, go head-to-head.
In the evening session match, scheduled to start at 8pm BST, the two winners from the first games, top seed Novak Djokovic of Serbia and Russia's Daniil Medvedev, the fourth seed, meet.
In today's round-robin doubles matches, third seeds Kevin Krawietz and Andreas Mies of Germany beat eighth seeds Lukasz Kubot of Poland and Marcelo Melo of Brazil 6-2 7-6 while fifth seeds Wesley Koolhof of The Netherlands and Nikola Mektic of Croatia beat second seeds Rajeev Ram of the United States and Joe Salisbury of Britain 7-6 6-0.