BEIJING, Oct. 5 -- World No.1 Rafael Nadal of Spain cruised past Karen Khachanov of Russia 6-3, 6-3 and local favorite Peng Shuai retired at the third round of China Open here on Thursday.

In the men's draw, Nadal broke Khachanov in the fourth game and raced to 4-1 lead to take control of the court in the first set. The 31-year-old, who won his third US Open title last month, maintained his momentum in the second set to seal the victory.

"I'm happy about the match today. I think I played a solid match," said Nadal, who will face John Isner of the United States in the quarter-finals tomorrow. The American big server stormed into the last eight with a 6-0, 6-3 win over Argentina's Leonardo Mayer.

The 27-year-old Romanian Sorana Cirstea upset the fourth seed Karolina Pliskova of Czech Republic 6-1, 7-5, also making it into the last eight. Cirstea will next take on Latvia's Jelena Ostapenko, the reigning French Open champion, who enjoyed a good start and stormed to a 3-0 lead before Peng calling for the timeout to deal with her knee injury. It's the first time Ostapenko advances to the quarterfinals of the China Open,

"Maybe recently there were ups and downs and several matches in a row that stressed it (knee injury)," Peng Shuai said after the match, "The doctor suggested I should take a period of rest and get it treated, but I can only rest after the season. I won't retire from tomorrow's doubles."

World No.3 Elina Svitolina of Ukraine beat Elena Vesnina of Russia in straight sets, 6-2, 7-5 in the third round in an hour and 49 minutes. Czech player Petra Kvitova, who ranked 18th in the world, defeated world number six Caroline Wozniacki of Denmark 6-1, 6-4 to reach China Open quarter-finals.