Juan Martin del Potro beat Russia's Karen Khachanov 6-4, 7-6(4) to reach the quarter-finals of the China Open on Wednesday while Grigor Dimitrov lost to unseeded Dusan Lajovic 6-4, 2-6, 6-4.
Victory meant US Open finalist Del Potro has sealed qualification for next month's season-ending ATP Finals in London, joining Rafael Nadal, Novak Djokovic and Roger Federer.
After cruising in the first set, Argentina's Del Potro faced a stern test in the next as Khachanov began to find his rhythm.
The Russian looked set to drag the contest into a decider but world number four Del Potro held his nerve in the tiebreak to close out the victory with an ace on match point.
Del Potro next takes on Serbia's Filip Krajinovic in the last eight after the Serbian overcame Spaniard Feliciano Lopez 7-6(5), 6-3. Del Potro beat Krajinovic in their only previous meeting in Miami earlier this season.
Krajinovic's compatriot Lajovic took advantage of Dimitrov's inconsistent serving to knock the world number eight out of the tournament in an hour and 50 minutes.
"The first set was hard to play because we had a shadow on the court... in the end it was a dog fight," Lajovic said after his second win over a top-10 player.
The 28-year-old Serbian next meets fifth seed Kyle Edmund after the Briton overcame Italy's Matteo Berrettini 7-5, 6-7(2), 7-5 in a tightly contested match lasting nearly three hours.
Former boxing world champion Rocchigiani dies in Italy
Germany's former world super-middleweight and light-heavyweight champion Graciano Rocchigiani has died aged 54 in southern Italy after being hit by a car while out walking, officials said on Tuesday.
The boxer, who had an Italian father and German mother, had held both the IBF super-middleweight title from 1988 to 1989 as well as the WBC light-heavyweight in 1998 by defeating Michael Nunn.
Rocchigiani, who fought all 48 of his professional fights in Germany, captivated the boxing world with his bouts against fellow German Henry Maske and Poland's Dariusz Michalczewski in the 1990s.
His last fight was in 2003 when he was defeated for the vacant WBC international light heavyweight title.
"Berlin mourns one of its athletes, who in the 1980s and 1990s fascinated the crowds," said Berlin mayor Michael Mueller in a statement.
"Rocky, as he was known around the world, was not only after Max Schmeling and Eckhard Dagge the third German world champion in the professional sport.
"He was also an original Berliner, who combined his mouth and his heart. Not everything worked out for him in life as it did in the ring. But Berliners loved him for his sometimes rough and edgy ways. We mourn a boxer with a big heart."
Rocchigiani, who had been imprisoned for assault and driving without a valid licence, had been the youngest German world boxing champion. He also worked as a boxing commentator.