WASHINGTON — Ramiro Pena hit a two-run homer off Craig Stammen with two outs in the 10th inning and the Atlanta Braves came back to beat the Washington Nationals 6-4 Friday night, stretching their winning streak to seven games. Pena, who reached on a bunt as a pinch hitter in the eighth, helped Atlanta finish off a rally in a game it trailed 4-0 after two innings and 4-2 entering the ninth. Eric O'Flaherty (2-0) pitched a 1-2-3 ninth for the win, while Craig Kimbrel retired the heart of Washington's order for his fifth save in five chances.