Second seed Novak Djokovic continued his imperious form in China with a 6-4 6-2 thrashing of Rainer Schuettler to reach the Shanghai Masters quarter-finals on Thursday.
As the debate about the draining effects of the long men's season continued, however, Stanislas Wawrinka and Gael Monfils became the sixth and seventh players to retire injured from the $3.24 million tournament.
By winning the season-ending Masters Cup here last year. the Serb proved that he has the legs to outlast his rivals.
The Serb won the China Open title last weekend and his victory over Schuettler, which set up a tie against Gilles Simon, was his ninth in a row on Chinese soil.
Spanish top seed Rafa Nadal overcame stubborn second-set resistance from compatriot Tommy Robredo to reach the Shanghai Masters quarter-finals 6-1 6-4 on Thursday.
World number two Nadal, still not back at his best after an injury-disrupted second half of the season, cantered through the first set but lost his serve at the start of the second.
The 23-year-old Australian Open champion however battled back into the set in a marathon third game before breaking again for a 5-4 lead and serving out for victory.