London - Rafael Nadal helped Stanislas Wawrinka seal a place in the semi-finals of the ATP World Tour Finals as the world number one defeated Tomas Berdych 6-4, 1-6, 6-3 on Friday.
Nadal had already qualified for the last four and his victory secured a first place finish in Group A of the prestigious season-ending event at London's O2 Arena.
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 victory over 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.
"I try to be intense in every moment. In the final set, I always enjoy to play these special moments."
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.
He had Berdych on the back foot with a series of blistering groundstrokes and converted his second break point to take the lead in the opening game of the match.
While it was Berdych who was fighting for a place in the last four, Nadal still needed to win one set to clinch top spot in the group and he showed no signs of taking it easy.
He held serve for the rest of the set and never gave Berdych a sniff of a chance to break back.
But at the start of the second set Nadal's concentration wavered and Berdych took advantage to break for a 2-0 lead.
Nadal was unable to break out of his sudden slump and Berdych broke to love in the fourth game before racing through the rest of the set.
It was the first time Nadal had dropped a set in the tournament, but the decider was far tighter.
Nadal had recovered his equilibrium and he gradually wore down Berdych, breaking for a 5-3 lead before serving out the win.