Johnson and Li entered the final day’s play tied on 16-under at the top of the leaderboard, and the American struck five birdies along with two bogeys to sign for a 67 in his final round and end the week on 19 under par.
Li, who edged a stroke ahead of Johnson before the turn but fell back after three bogeys on the back nine, settled for second place after carding a one-under-par 69 in his final round in King Abdullah Economic City.
Englishman Tom Lewis, who began the day by making five birdies in a row, finished third after signing for a 65 in his last round at the Royal Greens Golf and Country Club.
“It feels really good,” Johnson said. “Any time you can win a professional golf tournament, no matter where it is in the world, it’s a big win. I’m honoured to be the champion and I’m very pleased with the win.”
“The things that I’ve been working on are working and I’ve still got a lot of room for improvement. I’m very pleased with where the game is at. To get a win here… gives me a lot of confidence for the rest of the year.”
Johnson struck first against Li with a birdie on the par-four second to get his nose in front, but Li pegged the American back with a birdie on the fourth hole, before moving into the outright lead with another birdie on the ninth.