Singh, who won for the seventh time this season, is first for the second week in a row.
Tiger Woods, who was No. 1 for the last five years before coming in second to Singh last week at the Deutsche Bank Championship, remained in second, followed by Ernie Els and Masters champion Phil Mickelson.
Retief Goosen, the reigning U.S. Open winner, switched places with Davis Love III this week with the South African taking fifth and the American dropping to six.
Mike Weir, who blew a late lead at the Canadian Open, held on to seventh, while Padraig Harrington and Adam Scott also stayed pat at eighth and ninth, respectively. Stewart Cink, one of Hal Sutton's captain's pick for this week's Ryder Cup, moved up two to round out the top-10.
Jim Furyk and Sergio Garcia each fell one to 11th and 12th, respectively. Stuart Appleby maintained his 13th ranking, while Chad Campbell and Darren Clarke, who are on opposite sides this week at Oakland Hills, moved up to Nos. 14 and 15.
Kenny Perry sank two spots to 16. Chris DiMarco, British Open champion Todd Hamilton and Stephen Ames stayed where they were from last week. Miguel Angel Jimenez completed the top-20, jumping up one to supplant Scott Verplank.