London - Dominic Thiem kept alive his hopes of reaching the last four at the ATP Finals on Thursday, beating Kei Nishikori 6-1, 6-4 before pinning his hopes on a comprehensive win for Kevin Anderson over Roger Federer.
Coming into his final Lleyton Hewitt Group match, Thiem knew anything other than a straight-sets win would end his ambitions of reaching the semi-finals at London's O2 Arena.
The sixth seed must now wait for the result of the later encounter between Anderson and Federer to discover if he will advance.
If Anderson defeats six-time champion Federer in straight sets, the runner-up spot in the group will be decided by the percentage of games won between Federer, Nishikori and Thiem.
As a result of Thiem's straight-sets win, South Africa's Anderson has now qualified for the semi-finals.
"I just went into that match and wanted to show my real self again basically because two days ago was really bad," said Thiem, who lost in straight sets to both Anderson and Federer in his first two round-robin matches.
"I wanted to play well again," he added. "That's what I did part of times today in the match. Well, you never know what happens tonight, but I don't think it's going to happen."
Thiem started strongly, racing into a 3-0 lead after breaking serve in the second game of the match.
After surviving a tight fourth game, the Japanese number one quickly found his feet and soon threatened to retrieve the break of serve.
But Thiem found his best level when it mattered, saving four break points in the fifth game before breaking again immediately and going on to seal the set.
A single break in the seventh game of the second set was enough for Thiem to seal the match.
Nishikori won just 56 percent of points on his serve throughout the match and hit a total of 41 unforced errors, compared with 21 for Thiem.
Second seed Federer, looking to reach the semi-finals for the 15th time in 16 ATP Finals appearances, is 4-1 ahead in his head-to-head record against Anderson but lost to him in the quarter-finals at Wimbledon in a five-set classic.
Top seed Djokovic is already through to the semi-finals after beating Alexander Zverev in the Guga Kuerten Group, with Zverev, Marin Cilic and John Isner battling for the other semi-final berth.