Hunter Mahan fired a final-round 71 on Sunday to win the US PGA Tour\'s $6 million Houston Open by one stroke over Sweden\'s Carl Pettersson. Mahan, who won the elite World Golf Championships Match Play Championship in February, became the first two-time winner on the US tour this year. The victory will boost the 29-year-old to fourth in the world rankings, sending him into the Masters, the first major tournament of the season that starts Thursday at Augusta National, as the highest-ranked American. Mahan\'s one-under 71 at Redstone gave him a four-round total of 16-under 272. Pettersson also posted a 71 for 273. South African 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 on 274. Pettersson, who closed his round with eight straight pars, notched his second runner-up finish of the year.