BEIJING : Chinese tennis star Li Na cruised through to the quarter-finals of the Shenzhen Open on Wednesday with a straight sets victory over American Julia Cohen. The 2011 French Open singles winner and top seed took one hour and 34 minutes to defeat Cohen 6-3, 6-4. She will face Bojana Jovanovski in the next round. Li's compatriot Zhou Yimiao also powered through to the quarter-finals with a 4-6, 6-2, 7-6 victory over Chang Kai-Chen from Taiwan.