Serbia's Jelena Jankovic was ousted as world number one by compatriot Ana Ivanovic on Monday after holding the position for just one week.
Ivanovic, who was number one for nine weeks before Jankovic's brief reign, will retain top spot for at least three weeks, according to the WTA website.
The 20-year-old French Open champion pulled out of the Beijing Olympics last week with a right thumb injury. Jankovic lost to Russia's Dinara Safina in the quarter-finals.
Both will be playing in the US Open which starts next Monday.
