Hopes of a dream final between Rafael Nadal and Roger Federer were dashed on Friday when the top two seeds pulled out injured from their quarter-final matches at the Paris Masters.
Federer withdrew with a back injury a few hours before his match against American James Blake, while Nadal quit his showdown with world number six Nikolay Davydenko after losing the first set 6-1.
Wimbledon champion Nadal had the trainer massaging his right thigh and knee at the change of ends when trailing 4-1 and threw in the towel two games later.
The duo's exit left the tournament without any of its top four seeds after number three Novak Djokovic was beaten earlier in the week while fourth-ranked Andy Murray also perished on Friday, going down 7-6 6-3 to an inspired David Nalbandian.
Argentina's Nalbandian kept his Masters Cup hopes alive when he ended Murray's 14-match winning streak in the most spectacular match of the tournament and will meet Davydenko in the last four on Saturday.
Nalbandian, 14th in the ATP Race, will qualify for the season-ending tournament if he retains his Paris title. He was, however, reluctant to say if he would take part in the season-ending tournament he won in 2005.
"It's not my goal. I'm not thinking about Shanghai because we have the Davis Cup right after, so that's why," he said.
Nalbandian is scheduled to play the November 21-23 Davis Cup final with Argentina against Spain in Mar del Plata.
Federer was confident of defending his title in Shanghai despite his injury setback.
"I've had a lot of back pain over all the years of playing tennis... (but) it's just the first time it's acute during a tournament and it makes me pull out. I'll check it out for the next few days," the Swiss told reporters.
"The flight (to Shanghai) is scheduled for Monday. I hope I can recover ... otherwise I'll postpone that. I'm confident that hopefully it's going to get better in the next few days."
Nadal also struggled with aches and pains during his match and, unlike Federer, was unsure if he would be able to participate in the final event of the year.
Asked if he was worried about Shanghai, the Spaniard said: "For sure. Hopefully, it will be fine... (but) I don't know."
Nadal's retirement left the fans frustrated and they started booing when it was announced that Federer had handed Blake a walkover into the semi-finals.
Blake will now meet local favourite Jo-Wilfried Tsonga, who saved 10 break points in the second set en route to beating American Andy Roddick 5-7 6-4 7-6.
Both players need to reach the Paris final to book a trip to China for the Masters Cup, which starts on November 9.
Murray, who won the Madrid Masters and St Petersburg Open this month, struggled with his first serve in the opening set and smashed his racket to the ground after being broken in the fourth game.
The Scot then converted his only break chance to draw level and picked up his game, trying to keep Nalbandian at bay with his slice.
However, the Argentine, with a mix of cunning drop shots and powerful ground strokes, took the tiebreak 7-3.
Nalbandian then shifted up another gear, breaking four times in the second set to wrap up the victory.
"I thought the standard of points was excellent," said Murray. "I'm obviously disappointed to lose but I'm glad that I played against a guy as good as him and it took him playing a great match to beat me."
(Editing by Pritha Sarkar and Ken Ferris)