By Robert B. Waltz and Kamakshi Tandon

Ana Ivanovic's second-round exit has opened the door for the other four women still in contention for No. 1 at the US Open. Round by round, chart shows what must happen for them to reach the top spot – follow the top line to see how far into the tournament each would have to go, and look at the corresponding box to see which round her rivals must lose by.

For the record, Maria Sharapova was out of contention once she pulled out of the event, and Svetlana Kuznetsova's window of oppportunity closed afer Ivanovic won her first-round match.