BEIJING -- Juan Martin del Potro qualified for the ATP Finals for the fifth time by beating Karen Khachanov 6-4, 7-6 (4) Wednesday at the China Open.
Del Potro, who reached the US Open final this year, last qualified for the season-ending tournament for the top eight players in the world in 2013.
Del Potro will next meet Filip Krajinovic in the quarterfinals in Beijing. Krajinovic defeated Feliciano Lopez 7-6 (5), 6-3.
Also, third-seeded Grigor Dimitrov was beaten by Dusan Lajovic 6-4, 2-6, 6-4. Lajovic will next face fifth-seeded Kyle Edmund, who defeated qualifier Matteo Berrettini 7-5, 6-7 (2), 7-5.
In women's play, Karolina Pliskova advanced to the third round for the third consecutive year by beating Aliaksandra Sasnovich 6-3, 6-4.
The seventh-seeded Pliskova, who trailed 2-0 in the second set at the National Tennis Stadium before winning four games in a row, has lost in the third round the past two years in Beijing. She will next play local wild-card entry Wang Qiang.
Second-seeded Caroline Wozniacki earned the final spot in the third round with a 7-5, 6-3 victory over Petra Martic.
"I was just trying to stay focused and tried to run a lot of balls down, try to mix up the pace, be aggressive when I could," said Wozniacki, who will next play Anett Kontaveit.
Anastasija Sevastova became the first player to reach the quarterfinals by beating Donna Vekic 6-3, 6-2.