The American’s overall total of 261 was enough to hold off Li Haotong of China who came into the final round with a share of the lead after a third round that included four eagles.
The Chinese golfer shot a 1-under 69 Sunday, finishing a shot ahead of England’s Tom Lewis whose spirited last-round challenge was good enough to secure third another stroke back after a 5-under 65.
American Bryson Dechambeau, who won in Dubai last week, was joint sixth, eight shots behind Johnson after a 5-under 65.
The Saudi International is new to the European Tour and is being held amid scrutiny of Saudi Arabia’s human-rights record and condemnation following the killing of journalist Jamal Khashoggi.