Roger Federer bounces back and remains alive at the 2018 ATP Finals in London... for now.
Another defeat would have made it impossible for the Swiss to reach the semis but the six-time champion rebounded in style to post a classy win in which he lost only six points on serve.
Earlier, Nishikori (above) narrowly avoided only the second 6-0, 6-0 defeat in ATP Finals history against Kevin Anderson.
The 32-year-old won the first 11 games against Nishikori before his relieved opponent finally got on the scoreboard with an angled victor.
He added: "Important for me is to play a good last match here in the round-robin, try to beat Kevin".
"It feels good, I'm very happy I showed a reaction after the last match against Kei", Federer said. "I remember what a privilege it is to play here", he commented.
The Swiss star suffered a shock opening-round defeat against Nishikori before seeing off Thiem in straight sets in round two.More news: Recount Likely in Florida Governor Race
More news: Queen invites Meghan Markle's mother to spend Christmas with the royal family
More news: Free food on Election Day? Here's a list of Tuesday's delicious deals
"I don't know what happened against Nishikori. Sometimes, they go ask my agent", said Federer.
Anderson was brimming with confidence, being nearly untouchable on serve and made some powerful returns followed by loads of pulsating groundstroke to steamroll the Japanese No. 1, serving him a nice bagel and taking the opening set 6-0.
Federer snagged his first service break in the third game of the match and never looked back. Thiem did let rip with some stunning backhands but with the world number three back in the groove they made little impression as the Swiss sealed the 56th match win at the tournament he has qualified for a record 16 times.
Anderson is in pole position, but qualification for the semi-finals is still possible for all four players.
The South African, who had defeated Thiem on Sunday, needed less than an hour and five minutes to claim a hugely one-sided win, which he described as one of his "best ever".
"And I don't think there's a tournament director in the world who is not going to take those factors into account when setting the schedule".
"He was hitting the ball really well and it was making me impatient".