The 20-year-old Lewis led after the first round of the the British Open as an amateur this summer and he turned professional after the Walker Cup matches.
He quickly fulfilled the expectations placed on him by firing a closing-round 65 Sunday to win by two shots over third-round leader Rafael Cabrera-Bello. Lewis finished four rounds at the Oceanico Victoria course in 21-under 267.
Lewis had hoped to earn enough money in his limited number of pro starts this year to avoid having to go through the European Tour's qualifying tournament and a second-place finish in this event would likely have been good enough for him to reach that goal.
By winning, however, Lewis becomes automatically exempt from qualifying for the next two years.
Lewis birdied five consecutive holes beginning at the 12th to surge in front. He took the lead for good with a 30-foot birdie putt from the fringe at the par-3 16th.