Rafael Nadal secured top spot in Group A at the ATP Tour World Finals with a victory over Tomas Berdych that also sent Stanislas Wawrinka into the semi-finals.
Nadal had already qualified for the last four of the season-ending event at London's O2 Arena and his 6-4, 1-6, 6-3 win against Berdych ensured a first place finish with a 100 percent record from his three group matches.
Czech fifth seed Berdych could have gone through with a win, but instead he was eliminated and Swiss seventh seed Wawrinka progressed to the last four following his 6-7 (3/7), 6-4, 6-1 victory over Spanish third seed David Ferrer earlier on Friday.
Nadal's semi-final opponent on Sunday will be either old rival Roger Federer or Argentine fourth seed Juan Martin del Potro, depending on the winner of Saturday's Group B clash between those two.
Wawrinka, playing in the Tour Finals for the first time, will take on Group B winner Novak Djokovic in the other last four clash.
"Stan came to the locker room and said good luck. I said I would try my best. It's a good result for Stan. He's good friend of mine," said Nadal.
"I wish Tomas a good holiday and good luck for the Davis Cup final (against Serbia).
"In the second set he played great and it was very difficult to stop him."
With the number one spot in the year-end world rankings wrapped up after victories in his first two Group A matches, Nadal was free to focus fully on his bid to win the Tour Finals for the first time.
The 27-year-old has only made the final once, losing to Federer in 2010, but he would love to end that barren run and cap a remarkable return to action this year after seven months out with career-threatening knee tendinitis.
Nadal had won his last 15 meetings with Berdych and his last defeat against the Czech came way back in 2006, so it was hardly surprising to see the Spaniard seize the initiative at the start.
Berdych hit back to take the second set in emphatic fashion, but Nadal recovered well and landed the decisive break late in the deciding set.
Earlier, Wawrinka admitted he was pleased with his battling effort against Ferrer and was keeping his fingers crossed for a Nadal victory after winning in just over two and a quarter hours.
"Sure, tonight I will be a big fan of Rafa," Wawrinka said. "I did my job all week, did the best I could for all three matches.
"It's been an amazing week for me already. I beat Berdych, David Ferrer and I lost a tough one against Nadal. It was quite good level for me, that's the most important."