* Seven birdies in closing 67 * Fifth first-time winner in five events * Toms, McGirt finish one behind (Adds details, quotes) Nov 9 (Reuters) - Peter Malnati churned through the Mississippi mud to clinch a one-stroke victory at the $4.1 million Sanderson Farms Championship in Jackson on Monday. In his 22nd start on the PGA Tour, Malnati sank a three-foot par putt at the last to card 67 and finish at 18-under 270, edging fellow Americans David Toms (69) and William McGirt (68) at the soggy Country Club of Jackson. The PGA Tour sophomore, 28, became the fifth winner in as many tournaments in the new 2015-16 PGA Tour season, joining Emiliano Grillo (Frys.com Open), Smylie Kaufman (Las Vegas), Justin Thomas (CIMB Classic) and Russell Knox (WGC-HSBC Champions). More...