Nelson shot a 4-under 68 to edge Jim Ahern by one stroke in the Farmers Charity Classic at 14-under-par 202. The victory was Nelsons fourth of the season. Three weeks ago, he won the FleetBoston Classic for the second year in a row.
Nelson earned $210,000 for his triumph.
Nelson entered the final round in Ada, Mich., tied with Bob Gilder, but Gilder slipped into sixth place after a Sunday 73.
Ahern, whose first and only victory came in the 1999 AT&T Canada Senior Open Championship, took the lead by birdieing the 13th and 14th holes at Egypt Valley Country Club. However, he dropped a shot at the par-4 15th to fall to 13-under.
Nelson stood at 13-under before he hit the par-5 17th in two shots. He missed the eagle putt from eight feet, but tapped-in for birdie and the lead at 14-under.
Ahern missed a six-foot birdie putt at the par-4 home hole, giving Nelson two putts for the victory. Nelson rammed his birdie effort five feet past the hole, but made the comebacker to secure the title.
Full-field scores from the Farmers Charity Classic