Willett holed from 15 feet for a birdie on the 18th to card a closing 69 and finish 19 under par, one shot ahead of compatriot Andy Sullivan and playing partner Rafael Cabrera-Bello.
Sullivan had also birdied the last in the group ahead to temporarily join Willett at the top of the leaderboard, before Cabrera-Bello narrowly missed a long eagle attempt on 18 and tapped in for birdie to also finish 18 under.
Spain’s Alvaro Quiros and Korea’s Byeong Hun An shared fourth place on 16 under after matching rounds of 65, with defending champion Rory McIlroy another shot back alongside Henrik Stenson after also closing with a 65.
Willett had lost his overnight lead after a bogey on the second, but quickly found himself three in front thanks to three birdies in four holes from the fourth.
A bogey on the ninth allowed the chasing pack to close the gap, with Sullivan carding his third birdie of the day on the ninth to get within a shot, but Willett crucially saved par from a greenside bunker on the 11th and then doubled his lead on the next, holing from five feet for birdie on one of the hardest holes on the course.
A birdie on the par-five 13th took Willett three clear with just five holes to play, but the gap was suddenly cut to a single shot once more when Sullivan birdied the 15th to set up a birdie and Willett three-putted from just short of the green on the 14th.
Sullivan had saved par on the 16th after a wild drive in the trees and birdied the last to share the lead, but Willett left himself a slightly longer putt on almost exactly the same line and calmly holed for his fourth European Tour title.
The 28-year-old moves from 20th in the rankings to a provisional career-high of 12th, with the positions set to be confirmed after the conclusion of the Waste Management Phoenix Open on the PGA Tour.