It is Jankovic's second stint at the top of the rankings. She first reached the top spot in the rankings of Aug. 11 but slipped to No. 2 behind Serena Williams.
But Williams lost her first match at last week's Porsche Tennis Grand Prix in Germany while Jankovic ended up with the tournament title. The result lifted Jankovic, who won the tournament in Beijing the week before, to No. 1 and Williams is second.
"I am very happy that the hard work I've put in is paying off," Jankovic said after the win in Germany. "I've been playing very well since the U.S. Open and my confidence is quite high. I will try to do my best again next week and as I've repeatedly stated, my goal is to finish the season No. 1."
There were no other changes in the Top 10. After Jankovic and Williams came No. 3 Dinara Safina, fourth-rated Elena Dementieva and No. 5 Ana Ivanovic. The rest of the top tier has Maria Sharapova sixth followed by, in order, Svetlana Kuznetsova, Venus Williams, Vera Zvonareva and Agnieszka Radwanska. Nadia Petrova, who lost to Jankovic in the Porsche final, moved from 18th to 14th.