Guetz only managed an even-par 72 on Sunday, but he finished at 14-under-par 274.
That was only good for a one-shot victory over Smith, whose 10-under 62 established a new course record at National Pines Golf Club.
The past three weeks, Smith has gone 63-62-63 on Sunday and picked up a win and two runner-ups. His second-place finish this week gave him the money title and along with Spencer Levin, both earned exemptions to the second stage of the PGA TOURs national qualifying tournament this fall.
'That is huge,' said Smith. 'We did the math last night to see who could pass us with a good day, but I forgot about it when I went to the tee today. I'm a big advocate of this tour, it has done a lot for me and others before me. It's pretty special to win the Order of Merit.'
For Guetz, it was just special to get a victory.
'Finally,' joked Guetz. 'I knew someone was going to have a decent round, but that (Smith) was just crazy. That is the best round of golf I've seen in tournament play I've been involved with.'
Smith got in at minus-13 thanks to a chip-in birdie at the last. Guetz hung tough with three straight pars to polish off the victory.
John Ellis only managed a 72 and took third at minus-10. Mike Grob shot a 72 for fourth at 7-under par, one shot better than Joseph Lanza, who posted a 71 on Sunday.
Adam Bland (67), Graham DeLaet (71) and Rob Johnson (73) shared sixth at 4-under-par 283.