Wetterich now stands at No. 76 in the rankings. Immelman, meanwhile, climbed from No. 52 to 34th this week.
There was little change in the top 10 again. Tiger Woods easily remained No. 1 and was again followed by Phil Mickelson, Retief Goosen, Vijay Singh, Jim Furyk, Ernie Els and Sergio Garcia.
The first change came at No. 8 where Adam Scott moved up one spot after tying for third behind Wetterich. To make room for Scott, former PGA champion David Toms slipped one to No. 9.
Luke Donald held on to 10th, while Jose Maria Olazabal and Henrik Stenson were 11th and 12th again.
Chad Campbell jumped four positions to 13th this week. Chris DiMarco dipped one to 14, while David Howell was up one to No. 15. Geoff Ogilvy and Tim Clark each fell two places to 16th and 17th.
Stuart Appleby remained in the 18th slot. Davis Love III inched up a notch to 19 and Darren Clarke was up four to No. 20 this week. To make room for Clarke in the top 20, Fred Couples tumbled four places to 23rd.
Johan Edfors won the British Masters on Sunday for his second title on the European Tour this year. That win helped him move up 114 places to No. 80 in the new rankings.