Paris: Zheng Saisai and Xu Yifan hope to stay as long as they can at the French Open while the ninth-seeded Chinese tennis women's doubles pair vies for a berth at this summer's Rio Olympic Games. Zheng and Xu, ranked 21st and 23rd, respectively, in current WTA doubles standings released before the French Open, advanced to the women's doubles quarter-finals on Sunday after beating Aleksandra Krunic of Serbia/Mirjana Lucic-Baroni of Croatia 7-5, 7-5, reports Xinhua. The duo next play the winners between fourth seeds Timea Babos/Yaroslava Shvedova and Russian pair Margarita Gasparyan/Svetlana Kuznetsova. If through, Zheng and Xu will earn 780 points, and if not, an increase of 430 points will also do much to their rankings. According to the Olympic qualifying rules announced by the International Tennis Federation (ITF), top 10 players in doubles, partnering any one with a ranking, will be awarded direct passage to this summer's Olympics, which is impossible to Zheng and Xu. Then the remaining positions will be dispatched to top 14 pairs with highest combined rankings, with eight wildcards to complete the Olympic doubles main draw of 32 pairs. In London 2012 Games, the last pair owning a direct berth ranked a combined 102nd. "We really don't know how high the required ranking is to make sure an Olympic berth, so we just keep fighting to our limit to vie for more possible points," said Zheng. The 22-year-old and her partner Xu, who reached the last four at Australian Open in January, was playing their first clay-court Major as a pair, which's not easy for players like them, who grows up playing on hard court. "We've made a lot of efforts this season since aiming to qualify for the Olympic tennis tournament," added Zheng. "Some time Xu and I even gave up some singles play to make our doubles possible." Besides the women's doubles, the 28-year-old Xu also pairs up with Croatia's 117th-ranked Marin Draganja in mixed doubles at Roland Garros. "I found it fun playing mixed doubles which I'd never tried before," Xu said. "And also I think the mixed experience can help me improve skills in general doubles play, which may benefit the efforts of Saisai and I for Olympic berths."