The 41-year-old edged out Wang Jeung-hun by one shot after the South Korean teenager stumbled in the closing stages.
Wang led by three strokes at one point in the final round but he dropped shots at both the 17th and 18th, allowing Atwal to snatch victory with a birdie at the final hole.
Atwal finished with a six-under 66 for a four-round total of 16-under 272, while Wang carded a closing 67.
Scotland???s Simon Yates claimed third place, two shots behind Wang, after a four-under 68 in the final round.
Jake Higginbottom of Australia, whose 64 was the best round of the day, shared fourth spot with Thailand???s Thaworn Wiratchant (68) on 276.
Darren Clarke had moved into contention with a 64 on Saturday, but the Northern Irishman could only manage a level-par 72 which left him seven shots behind Atwal and tied for 15th place on 279.
English youngster Matthew Fitzpatrick finished on 280 after signing for a one-under 71.