Roger Federer and David Nalbandian secured semi-final places at the Masters Cup with victories in their final Red Group matches in Shanghai.
Federer has reached the semis for the fifth consecutive year
Defending champion Nalbandian knocked out Andy Roddick with a 6-2 7-6 (7-4) victory that also guaranteed world number one Federer's qualification.
Federer returned the favour, beating Ivan Ljubicic 7-6 (7-2) 6-4 to give Nalbandian second place in the group.
Rafael Nadal and Nikolay Davydenko face off for the final slot on Friday.
Nalbandian will face James Blake in the last four after the American qualified for the semi-finals by winning his opening two matches in the Gold Group.
MASTERS CUP SEMI-FINALS
Federer v Nadal/Davydenko
Blake v Nalbandian
"In the end what I care about is that I came through it, and not really who's the other guy," said Federer.
"But it's still a bit of a surprise, of course, that Nalbandian came through again.
"I guess he deserved it because he should have beaten Ljubicic yesterday and he beat Roddick convincingly today."
Knowing he had to win to have any chance of retaining his title, Nalbandian did an excellent job of defusing Roddick's big serve.
In this group, it's tough to win just one match
"In the beginning I played very good," said Nalbandian. "I was hitting good shots and got control of the match.
"He didn't serve so good, that's why I went away from him.
"In this group, it's tough to win just one match. Sometimes you need a little of luck."
And Nalbandian said it was difficult to enjoy the win after learning that his nine-year-old cousin and godson Lautaro Nalbandian had died in an accident at home in Argentina.
"It was terrible (but) I can do nothing from here," he said. "I try to push as hard as I can on the court."
Roddick, ranked fifth in the world, was a shadow of the player who came close to upsetting Federer on Tuesday.
"Give credit where credit's due - I didn't play badly, I hit the ball through the court, but he played very well," he said.
"Let's put it in perspective. Going into the summer, I think I was 18 in the champions race with people questioning if I would ever play top-level tennis again - I righted that."
Roddick joins Spain's Tommy Robredo in being eliminated from the tournament after defeat in the first two-set encounter in a tight group.
Red Group: Roger Federer (Swi), Ivan Ljubicic (Cro), Andy Roddick (USA), David Nalbandian (Arg)
Gold Group: Rafael Nadal (Spa), Nikolay Davydenko (Rus), Tommy Robredo (Spa), James Blake (USA)