Destinee Hooker, who was named tournament MVP, led the United States with 16 points, with Logan Tom and Jordan Larson adding 14 and 11, respectively.
For the first time the gold-medal match was officiated by two female referees: Zorica Bjelic of Serbia and Susana Rodriguez from Spain.
The United States started strongly in front of a packed Macau East Asian Games Dome, jumping out to a 9-3 lead. The Brazilian women steadily crawled their way back into the tie and were level at 17-17. It was tied again at 24-24 before Destinee Hooker smashed a ball home to give the Americans a second set point and Jordan Larson converted that with another kill on a counterattack.
The second set was also hotly contested before the United States surged away to earn a four point cushion at 19-15. After Brazil pulled to within two at 20-18, the United States concluded the set with a 5-2 run capped by a smart shot from Logan Tom.
Falling behind 9-4 early in the third set, the Brazilians fought hard to pull to within two at 23-21, only to see Foluke Akinradewo make it 24-21 with a short dink and Larson drive a ball out of bounds for the match winner.
"It is always a challenge to play the Brazil team; they are the best team in the world,” USA coach Hugh McCutcheon said. “For us, we had to play with a lot of discipline, focus on trying to work together and stick to the game plan."
"Our team really performed very well today. I am very proud of them, not just for the victory but also in every match played throughout this long tournament our team made improvement.”
Natalia Pereira scored 11 points and Sheilla Castro added 10 as the Brazilians, who were playing without Marianne Steinbrecher and Paula Pequeno due to injuries, finished second to the United States for the second year in a row.
"They gave us a lesson in volleyball tonight," Brazil coach José Roberto Guimarães said. "I agree with Fabiana that we were weak in our defense and blocking. We managed only two blocks in this entire match, and it is very hard to play the USA team like this. It is difficult to play against the USA because they play at a very high level and they are very consistent.”
Earlier on Sunday, World Grand Prix debutants Serbia overpowered reigning world champions Russia 25-21, 25-20, 25-16 in one hour and 17 minutes to win the bronze medal.
Serbian Jovana Brakocevic was the game’s top scorer with 17 points, while Natalya Goncharova earned 10 points for Russia.
"Today, I am very happy and very proud of my team,” Serbia coach Zoran Terzic said. “This is the first time Serbia participates in the FIVB World Grand Prix and we won the bronze medal. It is a great success especially as we won against a great team like Russia in a major competition."
It was Serbia who started the opening set stronger and they found themselves leading 8-5 at the first TTO with an ace by Brakocevic. However, a series of unexpected serving errors gave the Russians a chance to cut the deficit to one point. Awe-inspiring spikes from Brakocevic and Sanja Malagurski helped Serbia keep on course and take control. Before long, the Serbians extended their advantage from 11-9 to 16-9. The Russians used a 4-0 run to pull to within two at 23-21, but the Serbians carried the lead to the end of the set.
Serbia jumped into the second set aggressively leading 4-1 with Malagurski striking three successive sharp spikes from the wing, forcing the Russian coach to call a timeout. However, Russia did not lose touch with Serbia and counter-attacked with two concrete blocks to close the gap to two points. But Serbia powered on again as Malagurski continued her unstoppable spiking to help increase the margin to 22-16 and Rasic Milena earned Serbia another set with a hit down the middle.
The Russian women, who lost to Serbia 3-1 in their Pool A match on Thursday, put up no serious resistance in the third set.
"In the beginning of this tournament our aim was to see how our core players would perform in this competition, and we can see that our players still need a lot of improvement," Russia coach Vladimir Kuzyutkin said. "Although we did not get to the final or come away with the bronze medal, we are still happy for the opportunity to participate in this competition."