Rafael Nadal and Novak Djokovic were both tested on their way to the semi-finals of the Shanghai Masters.
New world No 1 Nadal had won all of his previous 22 sets against Stanislas Wawrinka, and he made that 24 unbeaten, but not without a big fight in the first set.
Wawrinka had three set points, two of them in the tie-break, but the deftest of drop shots from Nadal on the 21st point proved crucial.
The Swiss had break points in the first game of the second set but could not take them and after that it was largely one-way traffic as Nadal clinched a 7-6 (12/10) 6-1 victory.
The second seed next meets Juan Martin del Potro, who is one win away from qualifying for the Barclays ATP World Tour Finals in London next month.
The Argentinian defeated Spain’s Nicolas Almagro for the second time in as many weeks 6-3 6-3, dropping just five points on his first serve throughout the match.
Defending champion Djokovic dropped his first set of the tournament against Roger Federer’s conqueror Gael Monfils but recovered to win 6-7 (4/7) 6-2 6-4.
Monfils is always a crowd favourite because of his flamboyant style but he lost his way in the second set after being given a time violation.
The Frenchman continued to argue with umpire Carlos Bernardes, while he also called the trainer for treatment to what appeared to be a hip problem.
Monfils regrouped in the third set and held his own until Djokovic broke through for 4-3.
The Serbian said: “That was a very physical match. This is one of the fastest courts on the tour that we have so it’s quite suitable to his style of the game and he runs all over the place.
“He’s one of the best movers we have on tour but he’s not physically very fit so I knew after dropping the first set that he wouldn’t be able to hold that level so I just had to hang in there and stay tough and wait for my chances.”
Jo-Wilfried Tsonga boosted his hopes of playing at the O2 Arena with a comfortable 6-2 6-3 victory over Germany’s Florian Mayer.
The Frenchman is a big danger to Roger Federer in the race to qualify for the eight-man tournament, and another win in China would take him past the Swiss.