Martinez and Jerome scored in the win over Brazil to duplicate their feat in the 2-0 victory over Russia on Thursday.
Gyau, who lived up to his billing as one of the top young prospects the USA has produced in recent years, teamed up with Martinez for the first goal, and Jerome converted a penalty kick after he was taken down in the area late in the game.
Goalkeeper Earl Edwards contributed 10 saves to the winning effort. Brazil had a huge edge in play, outshooting the Americans, 19-6, but ended up with only nine players on the field after Matheus Carvalho and Guilherme were ejected in the last two minutes.
Two first-half goals from Ali Cukadar lifted Turkey to a 2-0 victory over the U.S. U-17s a day later on the final day of the Development Academy competition in Bradenton, Fla.
Only three starters against Brazil -- captain Jared Watts, midfielder Marlon Duran and forward Jack McInerney -- started against Turkey, which had lost its first two games, 7-2 and 4-3.
"Overall, it was a successful weekend," said Wilmer Cabrera, for whom the Nike Friendlies marked his debut as U.S. U-17 head coach. "We got two good wins, played well, and today we got a chance to look at some of our other players and evaluate them in an international game."
The U.S. U-17 '91 team swept all three games against U.S. club opponents, while the U.S. U-15 split squad teams finished with a 4-1-1 record.
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Dec. 8 in Bradenton, Fla.
USA 2 Brazil 0. Goals: Martinez (Gyau) 27, Jerome pen. 80.
USA -- Edwards, Arevalo (Polak, 35), Kitchen, Watts, Orozco, Gyau, Duran, Renken (Lemus, 59), Martinez, McInerney (Gutierrez, 73), Jerome (Craven, 90).
Brazil -- Luis Guilherme, Bernardo (Gerson, 52), Mauricio (Guilherme, 59), Venicius, Eron, Wellington (Jairo, 86), Belchoir (Fernando, 50), Elivelton, Coutinho, Matheus, Felipe (Danilo, 43).