PHOENIX -- Whenever Luis Castillo pitches, he typically puts the Mariners in a position to win. The issue is Seattle hasn't come out victorious as much as it would like when he is on the mound.

That wasn’t the case on Sunday afternoon at Chase Field.

The Mariners' offense backed Castillo, who struck out seven over his six scoreless innings, en route to a 4-0 win over the D-backs.

Seattle was just 3-7 in his 10 outings since the start of June, despite Castillo tossing six quality starts during that stretch. It’s a dilemma the Mariners have grappled with all season. They entered Sunday's finale just 6-5 in his quality starts and 9-12 behind him overall. Those numbers could cause frustration for some players, but Castillo always trusted his teammates.

“Even though we’re athletes, we have highs and lows. It’s just something we need to accept,” Castillo said to MLB.com in Spanish. “For me, it’s not frustrating. I trust all of my teammates in the clubhouse. I know every time they hit the field, they give it their all.”

Exactly one year ago, Castillo was acquired from the Reds to help the Mariners attempt to make the playoffs for the first time in 20 years. Since then, he signed an extension that keeps him in Seattle for five years, a place where Castillo feels comfortable professionally and personally. He’s bought into the organization's culture and he hopes to give the Mariners more winning seasons.

“It's been great,” Castillo said. “I've built a family here with this team. I just go out there, do my job. I keep trying to perform as much as I can when I'm on the mound. Hopefully, God gives me enough health to just continue to perform.”

“What a trade,” Mariners manager Scott Servais said. “Just kind of the whole turnaround of our pitching staff, and he is the rock. He's the guy we lean on and he showed up today.”

Seattle provided Castillo with some run support before he threw a pitch. The Mariners opened the scoring on Mike Ford's bases-loaded walk, then tacked on another with Ty France's RBI single in a two-run first. Seattle forced Arizona starter Merrill Kelly to throw 41 pitches in the opening frame, tied for the third most by any pitcher in the first inning this season.

“It gave me so much confidence,” Castillo said. “I came with more confidence in my pitch selection, commanding my strike zone and pitch location.”

J.P. Crawford made it 3-0 in the second inning with a solo home run into the bullpen in right field. Crawford finished 2-for-3 with two walks -- including one that kicked off that big first inning -- and three runs. But more than anything, he was relieved to help Castillo earn a win.

“He’s been pitching his [butt] off,” Crawford said. “He goes out there every time and gives a quality start. I’m happy we’re able to get some runs for him this time.”

The series win finished a two-city road trip on which the Mariners went 4-2 to improve to 54-51 overall. Seattle won six out of its eight series in July, but this was a particularly crucial weekend with the Trade Deadline looming Tuesday at 3 p.m. PT.

The Mariners are 4 1/2 games back of the final AL Wild Card spot. Next up, they return home for three games against the Red Sox, who sit two games ahead of Seattle in the postseason chase.

“You see what other teams are doing in our division, and you know, our guys want to go after it,” Servais said. “I credit them when they're super competitive, so that focus is tied to that. They know every at-bat counts, every inning counts. We've got to figure out a way to scratch and claw.

“They understand where we're at, and they want to push. They want to go for it, as they should.”