The 25-year-old zoomed to the top after her closest challenger for the position, Spain's Carolina Marin, lost in the India Open Super Series semifinal here.
Saina takes over the reins from China's Li Xuerui, thereby ending the Chinese stranglehold over the world rankings for many years.
Though the official rankings will be out only on Thursday next week, Saina has been assured of her ascent to the top owing to the reigning world champion's 19-21 23-21 20-22 loss to third seed Thai Ratchanok Intanon.
Saina plays Japan's Yui Hashimoto in the second semifinal but the Indian ace will be No. 1 irrespective of her result today.
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The London Olympic bronze-medallist has won a staggering 14 international titles in her glorious career and most recently she became the first Indian woman to make the finals of the prestigious All England Championships in Manchester
"Number one is not at the back of mind right now. The only thing I am focussing on is playing all the tournaments and I want to win them," Saina had said when asked about the ranking.