Indian tennis star Sania Mirza and her Swiss partner Martina Hingis won the St. Petersburg Ladies Trophy here on Sunday and extended their remarkable winning streak to 40 matches in the process.The top seeded Indo-Swiss pair hardly broke sweat on their way to a 6-3, 6-1 victory over the Russian-Czech team of Vera Dushevina and Barbora Krejcikova in the women's doubles final that lasted for an hour.This is the fourth title that Sania and Martina have won this year. Their overall trophy count now stands at 13. They started the year with wins in Brisbane and Sydney before completing a hat-trick of Grand Slam titles at the Australian Open.They have been close to unstoppable since an upset loss in the French Open quarter-finals last year. Since then, they have claimed titles at Wimbledon, US Open, Guangzhou, Wuhan, Beijing, the WTA Finals in Singapore, Brisbane and Sydney.