Casey, a nine-time winner on the European Tour, rose six places from last week.
Tiger Woods, Phil Mickelson, Sergio Garcia, Geoff Ogilvy and Padraig Harrington remained the top-five ranked players.
Casey was sixth and Vijay Singh fell one spot to No. 7, followed by Henrik Stenson, who moved up two to eighth. Robert Karlsson and Camilo Villegas both dipped two to round out the top 10.
Kenny Perry also fell two and is down to 11th. Steve Stricker inched down one to No. 12, but Lee Westwood climbed up a place to 13. Anthony Kim sank one to 14th and Jim Furyk held on to his 15th ranking.
Ernie Els, Rory McIlroy, Stewart Cink, Mike Weir and Martin Kaymer completed the top 20 once again.