Maggert shot a 5-under 65 at sun-drenched Del Paso Country Club, edging defending champion Colin Montgomerie by two strokes. Maggert made six birdies and one bogey to finish at 10-under 270.
The 51-year-old American won his first senior major last month in Alabama in the Regions Tradition. His only other Champions Tour victory came in Mississippi last year in his first start on the 50-and-over circuit.
Montgomerie closed with a 66. Grant Waite and Bernhard Langer tied for third at 7 under. Waite had a 67, and Langer, who shared the lead with Maggert after three rounds, shot a 68.
Lone Oak alum Kenny Perry shot a final round 71 and finished tied for 12th at 3 under. Paducah's Russ Cochran tied for 15th at 2 under after a final round 69. Metropolis, IL native John Riegger shot a final round 75 and finished tied for 38th at 4 over.