Kevin Anderson thrashed Kei Nishikori 6-0, 6-1 on Tuesday to move to the brink of the last four at the ATP Finals.
The 32-year-old South African was on the verge of completing just the second whitewash in the competition's history until Nishikori won the penultimate game.
Anderson, who lost just eight points on serve, could become the first African player to reach the semifinals of the season-ending tournament.
"Among the best I've played," Anderson said. "I think I did a really good job constantly applying the pressure and not letting up."
The only result from Tuesday's late match that can prevent the fourth-seeded Anderson from advancing would be a straight-sets victory for Roger Federer over Dominic Thiem.
Despite the resounding defeat, Nishikori's opening-match victory over Federer means he can still reach the semifinals for the third time.
"I'll try to forget about today," Nishikori said. "Something was wrong. I've got to fix it tomorrow and try to be positive for the next one."
Anderson and Nishikori split their last two meetings and the Japanese player held a 5-3 edge in their career head-to-head before this match. However, just as he did in his tournament-opening victory over Thiem on Sunday, Anderson started fast as an aggressive forehand into the corner earned him a 2-0 lead.
Having pledged to donate $100 to the Los Angeles Fire Department, who are fighting deadly wildfires in California, for every ace he struck, Anderson hit three in a row to consolidate the break.
"My coach is from California and so it's a bit more close to home," said Anderson, who ended the match with 10 aces. "We thought let's try — we will donate and do it in a way that is interactive."
As an increasingly frustrated Nishikori struggled to control his groundstrokes, Anderson displayed relentless accuracy to close out the opening set.
Nishikori took a lengthy break before the start of the second set, but it made no difference as Anderson ruthlessly raced to a 5-0 lead and moved to within one game of joining Federer in the history books. The six-time champion blanked Gaston Gaudio in Shanghai in 2005, but Nishikori finally put together a solid game.
Anderson, the Wimbledon finalist, swiftly completed his 47th win of the season, topping his career-high from 2015.
"Coming into this year I set my goals higher and I have embraced them well," Anderson said. "I have been able to stay the path throughout the year."
