(CNN) -- Rafael Nadal completed a perfect sweep of his matches in Group A of the ATP World Tour Finals by beating Tomas Berdych Friday -- his victory enabling a grateful Stanislas Wawrinka to accompany him into the semifinals in London.
Wawrinka and his supporters breathed a sigh of relief after Nadal wrapped up a 6-4 1-6 6-3 victory over his Czech opponent to go through as group winner.
The match had been in the balance when Berdych hit back to level at one set all with a display of power tennis that had the top seed wobbling, but he could not sustain the effort.
Nadal, who has never won the end of season showpiece, waited until the eighth game of the decider to make the breakthrough, taking advantage of two double faults by fifth seed Berdych.
He then served out for victory, completed with a flashing forehand winner and customary fist pump.
Nadal was also fully aware he had done Swiss star Wawrinka, who is making his debut in the finals, a big favor.
"I have a great relationship with him, so I'm happy for Stan, sorry for Thomas," Nadal said.
"Before the match Stan came to the locker room and told me 'come on', " he revealed.
Wawrinka, who would have been on the edge of the seat as Berdych made his move, tweeted: Vamooooos!!! Next diner is for me @RafaelNadal !! Good job!!
He had earlier battled past Nadal's compatriot David Ferrer in a thrilling afternoon match at the O2 Arena.
Wawrinka, who beat Berdych in his opening match before losing to Nadal, raced into a 5-2 lead in the opener before Ferrer battled back to force a tiebreaker, which he took 7-3.
But Wawrinka hit back to level the second set with a single break and then dominated the decider with two further breaks, sealing a 6-7 6-4 6-1 victory.
Saturday will see Group B decided with Roger Federer taking on Juan Martin Del Potro to decide who goes through to the last four with defending champion Novak Djokovic.
The Serb plays Richard Gasquet, who has already been eliminated.