The birdie finished off a 3-under 69 and left him one shot clear of both Andy Sullivan and Rafael Cabrera-Bello. It marks Willett's fourth on the European Tour since June 2012 and could move the Englishman as high as No. 12 when the newest world rankings are published.
"This one today showed some real guts," Willett said. "To get up-and-down from 95 yards (on No. 18) was just money."
Willett began the final round with a one-shot lead, and he grew it to a three-shot advantage at one point during the final round. But things started to tighten down the stretch, and after Sullivan and Cabrera-Bello both birdied No. 18, the tournament seemed to be headed for a three-way playoff.
Instead, Willett tallied one final birdie to clinch the victory, unleashed a fist pump and stamped his name as one to watch for the Olympics and the European Ryder Cup team later this year.
"They're two massive goals of mine," Willett said. "Just taking it day-by-day, week-by-week, and hopefully come August we'll be in Rio and come September we'll be with (Darren) Clarke at Hazeltine."
Sullivan was in search of his fourth win in the last 13 months, while Cabrera-Bello was a runner-up for the second straight week after being clipped by Branden Grace in Qatar.
World No. 2 Rory McIlroy closed with rounds of 68-65 over the weekend, but the Ulsterman was unable to overcome a slow start. He tied for sixth, four shots behind Willett and alongside Henrik Stenson.
"It's sort of a week of what could have been," McIlroy told reporters. "I played a lot of great shots and made a lot of birdies, but just made a few too many mistakes."