The 26-year-old Argentine, a surprise third at the British Open, fought through a steady downpour to produce a final round 2-under 70 and finish at 269. Denmark's Soren Hansen, who shot a 64, and England's Oliver Wilson finished three strokes back at 272.
Australian veteran Peter O'Malley was fourth -- five behind Romero after a final-round 65.
By the seventh hole, Romero already led by five strokes. His attacking style delighted the German spectators, as it did for fans watching the British Open. At Carnoustie, he collected 10 birdies in the final round before a two-stroke lead slipped away on the final two holes.
A drive into a soaked rough here produced a ninth hole double bogey, cutting his lead to two strokes, but steady golf afterward produced an easy victory, even though Romero didn't appear to play any hole safely.
'I try for a birdie on every hole,' Romero said. 'I have a lot of confidence after last week.'
A four-meter (12-feet) putt curved in for a final hole birdie for Romero, who won $810,000 and earned a five-year European tour exemption.
The Argentine recorded three eagles and 22 birdies at the event. On Sunday, it was so bad players left the protection of umbrellas only long enough to take a shot.
Romero's title came in his second year on the European Tour. His rookie season already drew attention, with four top-10 finishes, one of them a second at the Scottish Open.
Brett Wetterich finished tied seventh with a 70 and 276, along with another American, Charley Hoffman, who scored a final day 69.
South Africa's Rory Sabbatini, another player from the PGA TOUR, charged back from an opening day 78 to finish with a share of 11th at 277. He recorded a 68 Sunday after rounds of 65 and 66.