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Hunter Mahan fired a final-round 71 to win the US PGA Tour's $6 million Houston Open by one stroke over Sweden's Carl Pettersson.
The victory boost the 29-year-old to fourth in the world rankings, sending him into the Masters which starts at Augusta on Thursday, as the highest-ranked American.
Louis Oosthuizen, who led by two strokes after the third round, had two double-bogeys in a three-over 75 that left him in third place - two shots off the pace on 14-under par.
Three-time major champion Ernie Els needed a victory to earn an automatic invitation to Augusta.
Instead he was poised to miss the Masters for the first time since 1993 after finishing on 10-under par.
