Former world number one Maria Sharapova has bowed out of the Shenzhen Open tennis tournament. At Shenzhen, China, today, she lost to defending champion Katerina Siniakova of the Czech Republic in the semi-final. Siniakova, the sixth seed, beat the 30-year-old 6-2, 3-6, 6-3 and will face world number one Simona Halep in the final. Halep cruised into the decider in southern China with a comfortable 6-1, 6-4 victory over fellow Romanian Irina-Camelia Begu.Sharapova will return to the top 50 next week with the Australian Open looming at the end of the month, but she failed to reach her second final since returning last April after a drugs ban.Sharapova was banned for 15 months for taking the performance-enhancing substance meldonium, and has been working her way up the rankings since returning to action, winning the Tianjin Open in October.