Rafael Nadal came to Shanghai in high spirits and eyeing a 20th Masters title, but a shock defeat to Germany's Florian Mayer means he no longer has a chance of topping the year-end rankings.
For so long locked in a duel for tennis supremacy with Roger Federer, Nadal is now playing second fiddle to Novak Djokovic, who is guaranteed to end the year as world number one after Nadal's third-round defeat on Thursday.
A rueful Nadal said after his 6-7 (5/7), 3-6 loss to world number 23 Mayer that he came into the Shanghai Masters, missing Federer and Djokovic, in the right frame of mind after a good run, and defeat had hit him hard.
"For me today is a disappointing day. I felt that I did everything right. I was in the right line since the week before the US Open," said the Spaniard, who lost in last month's final at Flushing Meadows to Djokovic.
"I think I was doing everything right, practising with good motivation, practising well in general. I had a good result at the US Open. I had a good result last week."
The 25-year-old, beaten by Britain's Andy Murray in Sunday's Japan Open final, said defeat in Shanghai was a chance gone begging.
"It is an opportunity lost for me. To be at the top, to win tournaments, can happen less, you cannot lose opportunities. Today I felt I lost an opportunity to have a fantastic tournament here, and that's the negative part."
In a mixed season Nadal has lost seven out of 10 finals in 2011 and has won a single Grand Slam, the French Open, compared with three Slams in 2010, when he established himself as the unquestioned number one in the game.
"It's been a very positive season but at the same time a tough season for me. These kind of losses have an effect. It's normal," he said.
"If you are playing badly and you lose, it's fine. But my feeling is I was playing really well before the tournament. It is for that reason that the loss is tougher," he added.
Nadal said he had to "just accept the loss, accept that I have to keep working with the same line for the next two or three months, for the next season, and hopefully I can start the next season with more power, with a few things better".
Djokovic, the Australian Open, Wimbledon and US Open winner in 2011, took top spot in the rankings for the first time in his career when he deposed Nadal as All England Club champion in July.
Djokovic is the first player other than Federer (2004-07, 2009) or Nadal (2008, 2010) to finish number one since American Andy Roddick in 2003.