SEATTLE (AP) -- Washington rookie Kory Casto turned Father's Day into an even bigger celebration than normal with his first career home run.
"That's a pretty awesome thing the first one of my career on Father's Day and it was a go-ahead for the sweep home run," said Casto, who exchanged a quick hug with his father after the game. "That's a big deal. He [his father] told me it was a great present."
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 a fastball by 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.
"This is way bigger than I thought my first home run would ever be," said Casto, who grew up a Mariners fan. "It's a great feeling. The sweep's a bigger deal for us, playing well on the road and getting three from these guys."
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.
"I saw it go really high, I guess it hit the foul pole," Lowe said. "I saw it finish to the right of the foul pole. I thought it was foul when I saw it. The umpire had the good view and from what I heard it was fair."
Seattle right fielder Jeremy Reed and manager John McLaren briefly argued the call. Television replays showed the ball bounced off the foul pole.
Washington manager Manny Acta told Casto to get ready to pinch hit after Boone hit the double.
"I think Lowe has pretty good stuff and Wily has been struggling," Acta said of his decision to pinch hit. "We had to take a shot there and Kory was the best contact hitter we had."
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.
"Colome came in and was lights out," Acta said. "He had the best command of his fastball than he's had all season."
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.
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.
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. ... The Mariners were swept at home by an Interleague opponent for the first time since Interleague play began in 1997, a total of 36 home series.