MIAMI -- Of all their young starters, Sandy Alcantara has been the Marlins’ most consistent over the course of the entire season. On Sunday afternoon, the 24-year-old right-hander took another big step forward, and this time found himself back in the win column.

The hard-throwing right-hander was in complete control on Sunday and went the distance, while receiving ample run support in the Marlins’ 9-0 victory over the Royals at Marlins Park.

• Box score

For Alcantara, now 5-12, the victory was a long time coming, and it enabled Miami to salvage the series finale after dropping the first two. The win also was Alcantara’s first since June 21 at the Phillies. It also was his second complete game, with the other coming on May 19 in a 3-0 victory over the Mets in Miami.

“You want to see growth,” Marlins manager Don Mattingly said. “To see the growth from when he came up last year until now, that's a pretty big jump. You didn't really see it until you've seen this consistent run.”

• Young fan catches two foul balls in same at-bat

Despite going 12 starts between wins, Alcantara has progressively gotten better. Since Aug. 5, in seven starts his ERA is 2.77.

“I've come a long way,” said Alcantara, Miami’s lone All-Star. “I've had good days, bad days. But I never give up. I work hard to get better every time.”

Alcantara, Shane Bieber and Lucas Giolito are the only starters with two shutouts this year.

Miami’s offensive onslaught started with Starlin Castro’s one-out home run in the first off left-hander Mike Montgomery. Castro added an RBI double, while Harold Ramirez and Lewis Brinson each had two RBIs. Every position-player starter had at least one hit.

“Castro just lifted us up with a homer, and everybody contributed,” said first baseman Martín Prado, who went 1-for-3. “But, behind that, Sandy was outstanding. When you have a guy who is locked in, he's kept us in games. When you have a guy like that pitching that way, we all feed off him. Overall, good team win.”

In the eyes of the organization, Alcantara is scratching the surface of what he can become. The efficiency the rookie showed on Sunday is a reminder.

“I felt extremely good today,” Alcantara said. “Inning by inning, getting on the mound and instead of thinking about finishing the game, just attack the hitters. I thought about throwing first-pitch strikes and getting strikeouts.”

Entering the ninth inning at 89 pitches, Alcantara ended up with 102, with 74 strikes. The right-hander struck out eight and scattered four hits and two walks.

“You've got to give credit to their starter,” Montgomery said. “He set the tone for that game. Stuff wise, unbelievable. Making good pitches, and he had us on our heels."

Alcantara is the third Marlins rookie to post two shutouts in a season, joining Dontrelle Willis in 2003. He’s also the third rookie in club history to have two complete games. Anibal Sanchez (‘06) and Willis (‘03) also did it.

Through two innings, he was at 25 pitches with 23 strikes, and he didn’t allow a baserunner until one out in the fourth inning on Adalberto Mondesi’s single to center.

Alcantara attacked with his power sinker, which maxed at 97.1 mph, and he induced 10 ground-ball outs.

“When I see a pitcher command a fastball like he was commanding it today, it makes the secondary pitches more effective,” Prado said. “He just settled his fastball the first couple of innings, and his secondary pitches became big for him.”

Alcantara also benefited by a rare day of run support. He came into the contest averaging 2.60 runs of support, the lowest in the Majors among starters. The next closest is Miles Mikolas of the Cardinals, 3.76.

How significant is the support issue? Alcantara’s 2.60 is the fewest among qualified starters in the Majors since Shelby Miller received 2.54 runs of support in 2015.

Before Sunday, only once in Alcantara’s first 27 starts did the Marlins score more than five runs in any of his starts, which came on June 5 in a 8-3 win at Milwaukee.

“You could see it early, [he was] aggressive,” Mattingly said of Alcantara. “Low pitch count. A lot of contact and on the attack. Actually swing and miss, too. He had his pitch count in a good area. You knew you had a shot [at a complete game], if this thing kept going to be able to finish it.”