Lopes, 25, wearing a glittery strapless gown with feathery fringe, accepted the crown yesterday from last year's winner, Mexico's Ximena Navarrete, after upsetting a line-up of Latin American beauties who had been favored to win.
Ninety-eight young women took part in the contest -- in South America's largest city, Brazil's industrial hub of Sao Paulo -- watched by an estimated one billion people around the world.
"Now I have work to do, and I want to try to keep my feet on the ground," Lopes told reporters as she struggled to hold back tears after receiving a standing ovation at Sao Paulo's Credicard Hall.
Earlier, when the judges asked what physical trait about herself she would change if given the opportunity, she replied: "Nothing, I am satisfied with what God gave me," and added that it was important to have "inner beauty."
She will go on to serve as a world ambassador of sorts, with a full calendar of public appearances to raise awareness about the fight against AIDS and other serious diseases.
It was the ninth time the competition was held in Latin America but the first time it was hosted by Brazil.
Latin American women were the favorites this year after winning the crown in seven of the last 10 competitions, and all eyes were on the slender Vanessa Goncalves of Venezuela, which has a highly competitive beauty pageant circuit.