SEATTLE, Wash. -- Rookie Kory Casto's pinch-hit, three-run homer off the foul pole broke an eighth inning tie and led the Washington Nationals to a 6-2 win over the Seattle Mariners on Sunday. The Nationals swept their first three-game series since last September and handed the Mariners their seventh consecutive home loss. It is the longest home losing streak for the Mariners since they lost eight straight in 1996 at the Kingdome. Casto's first career homer came off reliever Mark Lowe (1-3). Casto, who grew up in Salem, Ore., was 0-for-14 in his previous five games. Washington recalled him June 3 from Triple-A Columbus. Reliever Jesus Colome (2-1) picked up the win. He threw two innings of scoreless ball in the seventh and eighth.