Roger Federer thrashed Andy Murray 6-0 6-1 to end the Briton's ATP World Tour Finals hopes in humiliating fashion.
The 17-time Grand Slam champion needed just 56 minutes to win his third Group B match and reach the semi-finals.
Murray required a straight-sets win to qualify but won only eight points in the first set and did not win a game until 6-0 5-0 down.
The result is Murray's worst since he lost 6-1 6-0 to Novak Djokovic in Miami seven years ago.
Japanese world number five Kei Nishikori qualifies behind Federer after his earlier 4-6 6-4 6-1 victory over Spaniard David Ferrer - a replacement for the injured Milos Raonic.
"Clearly, I'm very happy to play a good match today," Federer said. "I knew I was qualified so maybe I went in a bit more relaxed.
"It's not the way I thought it was going to go, but there's always next year for Andy and hopefully he can have a good season.
"At the end I was happy I didn't win the second to last game to be quite honest."
After 24 minutes, Murray's progress in the tournament was over as he suffered his first 6-0 set loss in four years.
"It was a tough night," Murray said.
"I've lost Grand Slam finals, which have been very tough, but in terms of the way the match went it was not ideal from my side of the court - far from it.
"He played exceptionally well, that's for sure. I can say I'm disappointed with my level tonight but if I played well, he probably still would have won anyway."
A tight, tense encounter had been anticipated with the Scot needing a fast start, and Federer keen to win the group and so probably avoid top seed Novak Djokovic in the semi-finals.
In the event, only one player brought anything like his best game
The 17,000 spectators packed into the O2 must have thought they were in a for classic when Murray won the opening two points on Federer's serve, before the Swiss won an epic 34-stroke rally on the third.
From that moment on it was one-way traffic as Murray struggled to find first serves and Federer produced some sublime tennis.
As the games rolled by, he even threatened to inflict the dreaded 'double bagel' on Murray, whose ambition became drastically reduced.
"Just try and win the point," he said. "Try and set a target of winning points. Try and win two points in a row rather than trying to focus on, 'OK, I want to get this game.'
"You just try and set smaller goals than that. That's basically it."
Federer moves on to the semi-finals and keeps his outside hopes of ending the year as world number one alive, although Djokovic can end that race should he beat Tomas Berdych on Friday.