Teacher:In this task, you are given an article. Your task is to summarize the article in a sentence.
Teacher: Now, understand the problem? Solve this instance: The world number one took his record in Beijing to 26-0 in five visits as he beat China's number one 6-2 6-1.
Djokovic, 28, goes on to face Australian John Millman or American John Isner in the last eight.
Croatia's Ivo Karlovic became the all-time leader in aces as he hit 26 to reach 10,247, passing compatriot Goran Ivanisevic's record of 10,237.
"It's a great feeling," said 36-year-old Karlovic. "For the past year I knew it was possible and I was hoping that it would be this year. It's great that it happened here.
"I'm not done yet. There are many years in front of me and hopefully that number will go up and up."
Another strong serving display did not prevent the 6ft 11in Karlovic losing 7-6 (7-5) 7-6 (9-7) to Uruguay's Pablo Cuevas, however.
Third seed Rafael Nadal is already though to the quarter-finals, where he will face American Jack Sock on Friday.
In the women's event, Spain's Garbine Muguruza sealed her place in the end-of-season WTA Finals with a 1-6 6-2 6-1 win over Croatian Mirjana Lucic-Baroni.
The 22-year-old joins Simona Halep and Maria Sharapova in the singles field of eight, with five more spots yet to be determined.
Russia's Anastasia Pavlyuchenkova beat US Open and third seed Flavia Pennetta 3-6 6-4 6-3, while US Open finalist and fellow Italian Roberta Vinci went down  6-1 3-6 6-2 to American Bethanie Mattek-Sands.
Student:
Novak Djokovic raced into the quarter-finals of the China Open with a 55-minute win over home hope Zhang Ze.