JAKARTA, Aug. 13 (Xinhua) -- Defending singles champions Chen Long of China and Carolina Marin of Denmark advanced to the quarterfinals at the badminton world championships on Thursday.

The top-seeded Long defeated Tanongsak Saensomboonsuk of Thailand 21-17, 21-18 and will next face either seventh-seeded Viktor Axelsen of Denmark or 11th-seeded Prannoy Haseena Kumar of India.

His compatriot Lin Dan, seeded number 5, also reached the quarterfinals after defeating Hans Kristian Vittinghus from Denmark.

In women's singles, Marin struggled to beat Pai Yu Po of Chinese Taipei 21-11, 18-21, 21-17. She will next play seventh-seeded Wang Shixian of China, who defeated 15th-seeded Busanan Ongbumrungpan of Thailand 24-22, 21-11.

In mixed doubles group, three of China's seeded pairings successfully secured berths in the quarterfinals. They are No. 1 Zhang Nan/Zhao Yunlei, No. 4 Liu Chen/ Bao Yixin and No. 2 Xu Chen/Ma Jin.

Seasoned player Lee Chong Wei from Malaysia knocked out China's Wang Zhengming 21-17, 21-19 to advance into the quarterfinals.

Lee is playing at the world championships as a non-seeded player as he has been stripped of his BWF seeding due to doping allegation. He had just served out an eight-month suspension.