Rafael Nadal held off Tomas Berdych 6-4, 1-6, 6-3 to finish the round robin 3-0 and win his group at the ATP World Tour Finals, allowing Stanislas Wawrinka to join him in the last four.
Wawrinka beat David Ferrer 6-7 (3), 6-4, 6-1, but needed Nadal to win to advance to the semifinal.
Nadal lost his grip on the match in the second set, dropping his serve twice. The Spaniard had already qualified from Group A after winning his first two matches, clinching the year-end No. 1 ranking the process.
Nadal only needed to claim a set against Berdych to clinch the group win. But he broke him in the eighth game of the third set after Berdych double-faulted twice.
"I wish him a good holiday and good luck for the Davis Cup," Nadal said of Berdych, who will be playing in next week's Davis Cup final between defending champion Czech Republic and Novak Djokovic's Serbia in Belgrade. "In the second set he played great, it was very difficult to stop him."
Against Ferrer, Wawrinka hit 35 winners, including 12 aces, to clinch his second win at the season-ending tournament.
Defending champion Novak Djokovic has won Group B. The winner of Saturday's match between Juan Martin del Potro and Roger Federer will join him in the semifinals.