SEATTLE — For the second time in three games, a contest between the Seattle Mariners and Arizona Diamondbacks came down to extra innings Sunday at T-Mobile Park.

For the second time in three games, the Mariners came on top. They beat the Diamondbacks 3-2, courtesy of a walk-off RBI single from designated hitter Victor Robles in the bottom of the 10th.

Seattle improved to 31-29 with the win, secured its sixth-straight win and second consecutive series sweep and moved up to 2.5 games over the Athletics and Texas Rangers for first place in the American League West.

It was the first walk-off of Robles' major league career.

"(Robles) brings a lot of energy. Brings a lot of excitement," Mariners manager Dan Wilson said in a postgame interview Sunday. "He got up there in the big moment today and I thought his approach was good — try to hit it up through the middle of the field. ... What we've seen from Vic since he's been back (from injury) has been outstanding. We saw him sting a lot of balls in Sacramento and getting a chance here today."

Seattle did what it did the entire weekend — get ahead and get ahead early.

Mariners second baseman Cole Young hit a solo home run to right field in the bottom of the second inning and gave the team a 1-0 lead.

The sole run was enough breathing room for Seattle starting pitcher Bryce Miller, who was working in piggyback tandem with fellow starter Luis Castillo for the third time through the order.

Sunday marked Miller's second time starting between the two in the piggyback arrangement. Both times he hasn't allowed a run.

Miller finished his outing with six strikeouts, one walk and one hit allowed in five innings pitched.

"We, I think the first however many games, never really played to our potential, I don't think," Miller said after the game. "We knew, even the games that we won, either we wouldn't pitch that well or wouldn't hit that well. Whenever this all clicks, we're gonna be a really good team. ... We still have room to get better. Hopefully we're hitting a stride (and can) keep it rolling."

Arizona's first run didn't come until Luis Castillo was in for his respective outing.

In the top of the sixth, Diamondbacks right fielder Corbin Carroll scored on a wild pitch from third with two outs to tie the game 1-1.

The tie didn't last long. Designated hitter Dominic Canzone (who Robles entered for as a pinch-runner later in the game before being subbed in in the lineup) hit the Mariners' 10th home run in three games — a solo shot to right field — to give his team a 2-1 lead.

Arizona second baseman and former Seattle player Ketel Marte, who was held hitless across the three-game series, brought the game back even 2-2 with an RBI sacrifice fly in the top of the eighth, which ultimately sent the game into extra innings.

Castillo came back out for the 10th inning. Due to the MLB's extra-inning regular season rules, Sunday was the first time in his career he inherited a runner as a reliever. 

The three-time All-Star didn't allow that runner to cross. After walking catcher Gabriel Moreno following a sacrifice bunt, Castillo struck out pinch-hitter Adrian Del Castillo and induced a groundout from Marte to leave runners stranded at the corners for the Diamondbacks.

Castillo finished his outing with three fanned batters, two walks and two runs allowed (one earned) on two hits in five innings pitched. Both he and Miller threw five innings and 71 pitches each.

"For me, I think it was an excellent outing," Castillo said via interpreter Freddy Llanos in a postgame interview. "We went out there and just battled and battled in a very close game. There were a couple obstacles but the good thing for me is we were able to overcome them. The important thing for me is I'm healthy and we're throwing the ball right."

M's right fielder Luke Raley was intentionally walked to lead off the bottom of the 10th. Young laid down a sac bunt, which set up Robles for the walk-off single.

The Mariners will look to extend their win streak to seven games and hopefully begin the process of a third-straight sweep in the first of a three-game series against the New York Mets at 6:40 p.m. PT on Monday at T-Mobile Park.

Emerson Hancock will start for Seattle and Austin Warren will start for New York.

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