Westwood won the Thai event by seven strokes for his career 37th tournament win. The Thailand Golf Championship is on the Asian Tour calendar. Westwood won the Indonesian Masters on the same tour last January.
That allows Westwood to go ahead of McIlroy in the rankings, although he still is well behind world No. 1 Luke Donald.
Donald has a rankings point average of average of 10.027 with Westwood at 8.063 and McIlroy in third at 7.772.
The next five places are the same this week with Martin Kaymer (6.550) in fourth and Adam Scott (5.496) taking the No. 5 spot. Steve Stricker is sixth with an average of 5.329 while Dustin Johnson (5.273) is seventh and Jason Day (5.071) is eighth.
Charl Schwartzel, who was second to Westwood in Thailand, goes from 11th to No. 9 with an average of 5.060. That pushes Webb Simpson (5.028) and Matt Kuchar (4.711) both down one spot to 10th and 11th, respectively.
Ian Poulter, who won the JBWere Masters in Australia, jumps from 28th to No. 16 in the rankings.