The Austrian, beaten by Kevin Anderson and Roger Federer in his opening two round-robin matches, knew only a straight sets victory would suffice and he delivered with a positive display.
Dominic Thiem claimed his first win of the week at the ATP Finals as he beat Japan's Kei Nishikori 6-1 6-4 to stay mathematically alive at the O2 Arena on Thursday.
The Austrian, beaten by Kevin Anderson and Roger Federer in his opening two round-robin matches, knew only a straight sets victory would suffice and he delivered with a positive display. He dominated throughout with Nishikori, who can no longer reach the semis, guilty of 41 unforced errors.
Thiem needs South African debutant Anderson, who is guaranteed a semi-final spot, to beat six-times champion Roger Federer for the loss of less than six games to make the semis.
Federer, who bounced back from his surprise loss against Nishikori to beat Thiem in his second match, can still top the group and avoid a potential semi-final with world number one Novak Djokovic by beating Anderson.
The Swiss is looking to reach the semi-finals for the 15th time in 16 appearances at the ATP's prestigious year-ender.
After describing his error-strewn loss to Federer as 'unacceptable', Thiem produced a performance much more in keeping with a player who reached the French Open final this year and who has now won 54 matches during the season.
"I didn't come into the match with too much pressure," said Thiem in his on-court interview. "I just wanted to show to myself and all the spectators the real Dominic Thiem."
Thiem won the opening three games, but had to save three break points at 3-1 as Nishikori briefly raised his tempo.
The Austrian world number eight captured another break to take the first set. A superb backhand winner then gave him the one break of serve he needed at 3-3 in the second set.
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 "Dominic Thiem in action on Thursday")
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