In doing so he went past the likes of Ben Hogan, Byron Nelson, Sam Snead and Arnold Palmer, who all won three of the US tour's four Texas events but never clinched the full set of Byron Nelson, Texas Open, Houston Open and Colonial titles.
Scott and Dufner both fired final round four-under-par 66s to finish locked at nine-under, forcing the playoff.
When he teed off in the final round, Scott was tied 16th and knew he needed to finish inside the top 13 to hold on to the No1 ranking following world No3 Henrik Stenson's tie for seventh on the European Tour.
By the time he made a clutch 4m putt on the second playoff hole for birdie and then a 2m winner the next hole, he had opened up a handy rankings cushion that will make him hard to topple before next month's US Open.
"It was certainly on my mind," said Scott of the rankings battle. "But I think the important thing was I realised that [being No1] didn't mean playing perfect. The way I came back and got it done, I felt like I certainly played like one of the best players in the world out there."
While he completed the Texas Slam by adding to his 2007 Houston Open, 2008 Byron Nelson Championship and 2010 Texas Open, he has his sights on a career major championship grand slam. Right now his 2013 Masters win is his only major title.
Rounding out a great day for the Australians, John Senden finished tied fifth and clinched a US Open start through his world ranking, and Matt Jones has a place in his first British Open and a second US Open.
- AAP