SEATTLE (AP) - 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.

Aaron Boone led off the eighth with a double, he advanced to third on Felipe Lopez's sacrifice bunt. Lopez reached first on the play. Casto, pinch-hitting for Wily Mo Pena, homered to right on an 0-1 count.

The Nationals added another run on Lastings Milledge's sacrifice fly.

Reliever Jesus Colome (2-1) picked up the win. He threw two scoreless innings.

The Nationals tied the game at 2-2 in the seventh on a ground-out RBI by Jesus Flores that scored Cristian Guzman. Guzman had doubled and advanced to third on an infield single.

Washington starter Tim Redding allowed two runs and five hits in six innings. He struck out four and walked two.

Seattle starter Jarrod Washburn gave up two runs and eight hits in six innings before Lowe relieved him with two runners on in the sixth.

Seattle took a 2-1 lead in the fourth on an RBI-single by Ichiro Suzuki that scored Willie Bloomquist. Bloomquist hit a two-out single and stole second.

The Mariners scored an unearned run in the third to tie the game at 1-1 when right fielder Elijah Dukes dropped a fly ball hit by Jose Vidro with two outs that allowed Jose Lopez to score from third. Lopez reached base when second baseman Felipe Lopez dropped a grounder for one error and then threw the ball past first baseman Aaron Boone for a second error.

The Nationals, who have won three straight games for the first time since a four-game winning streak April 27 to May 1, took a 1-0 lead in the first on a ground-out RBI by Flores. Notes: Seattle manager John McLaren shook up the bottom of the lineup for the final game of the series with Miguel Cairo, Jeremy Reed and Willie Bloomquist starting for Richie Sexson, Wladimir Balentien and Yuniesky Betancourt. "We just wanted to get a different look out there," McLaren said before the game. ... By placing pitcher Odalis Perez on the DL Friday, five of the eight Nationals on the DL were starters in the season opener. ... Umpire Jerry Crawford returned to work Sunday. He left Saturday's game in the third inning with back spasms.