Williams on Monday marks her 10th consecutive week atop the rankings. She's been No. 1 for a total of 133 weeks, which is sixth most all-time. She has 11,115 rankings points but isn't entered in either WTA tournament this week.
The Porsche Tennis Grand Prix still features seven Top 10 players, including defending champion Maria Sharapova, who is No. 2 in the rankings. However, No. 3-ranked Victoria Azarenka, the tournament runner-up last year, and fourth-ranked Agnieszka Radwanska, who was a 2012 semifinalist, aren't in the field this week.
Williams has an 875-point lead over Sharapova, who has 10,240 points, for the No. 1 ranking while Azarenka has 9,325 points and Radwanska 6,845.
In addition to the Porsche Tennis Grand Prix, the WTA has a tournament this week in Morocco. World No. 15 Dominika Cibulkova is seeded first there.