Sania Mirza and Martina Hingis failed to defend their prestigious WTA Finals title, as they bowed out in the semifinals Saturday night from the event being played in Singapore.In last-4 stage, Indo-Swiss pair lost to Russian duo of Ekaterina Makarova and Elena Vesnina as they came back from a set down to upset the defending champions to reach their first final. Sania and Hingis gave up the initial lead as the scorecard read 3-6, 6-2, 10-6 in Russian teams' favour. Makarova and Vesnina are set to face Lucie Safarova and Bethanie Mattek-Sands in the final of the event today.With a loss in the year ending WTA Finals, Sania's reign as doubles World number one is thrown into question. This was Sania and Hingis' first competition since they had split following an early exit at Montreal in July.