Siem was a wire-to-wire winner at the Trophee Hassan II event in Morocco, but Russell Henley posted a 4-under-par 68 that boosted him to a tie for 20th in the PGA Tour's Shell Houston Open -- just enough to keep him in the Top 50 while Siem, who opened the week ranked 72nd, is now 51st.
Henley's ranking point average is 2.37 while Siem's rounds out to 2.35.
Players ranked in the Top 50 are invited to the Masters, which begins April 11. Last week's tournaments marked the final chance for players to reach that threshold.
The only change in the Top 10 this week has Phil Mickelson getting the No. 10 ranking, passing Keegan Bradley despite the fact that Bradley tied for 10th in Houston and Mickelson was a stroke back tied for 16th.
D.A. Points won the Houston tournament, getting his second PGA title and going from 195th to No. 70 in the rankings.
Tiger Woods is No. 1 for a 624th week. He has a rankings points average of 11.75. Rory McIlroy (10.87) is ranked No. 2. Justin Rose (7.01) comes in third with Luke Donald (6.69) fourth and Brandt Snedeker, at 6.29, ranked fifth.
Louis Oosthuizen has an average of 6.06, which is sixth highest. Adam Scott's average of 5.70 is No. 7, ahead of Steve Stricker (5.69) and Matt Kucher (5.30). Mickleson's average is 5.25 and Bradley's is 5.22.