ST. LOUIS -- Elieser Hernandez on Monday made his second straight spot start for the Marlins, and the way he is throwing, the 23-year-old is building a case to stick around awhile.

Facing the Cardinals for the second time in six days, Hernandez allowed two runs, with one earned, in six innings with six strikeouts and no walks. But a lack of support proved costly, and the Cardinals, backed by Matt Carpenter’s home run, claimed a 5-0 win in the four-game series opener at Busch Stadium.

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“Really good,” Marlins manager Don Mattingly said of Hernandez. “I'm really happy with his outing. He was aggressive, throwing strikes. Mixing pitches. Really good to see.”

Hernandez is another young, talented starter who had a 1.13 ERA in nine starts at Triple-A New Orleans before getting another shot in the big leagues.

“We've always talked about him, he's a sharp kid,” Mattingly said. “He pitches fearlessly. Throwing strikes. On the attack. Using all of his pitches. A pitch up, a pitch down. Slider. Changeup. He threw the ball well.”

Hernandez got a taste of starting as a rookie in 2018, making six starts to go along with 26 relief appearances. Monday was the eighth start of the right-hander’s MLB career, and the six innings establish a personal high.

“I'm just following the same plan,” Hernandez said through an interpreter. “I'm just trying to have fun, and help the team win some games.”

Carpenter opened the scoring with a home run with one out in the third inning.

Carpenter came into the game hitting .102 against offspeed pitches. The changeup, according to Statcast, is in the offspeed category. But Hernandez elevated a changeup, and Carpenter didn’t miss it.

“It was a little bit higher,” Hernandez said. “I made a mistake.”

And Carpenter set up St. Louis’ second run with a bunt double to a vacated left side of the infield due to Miami’s infield shift.

“Any time that there is not somebody over there with less than two strikes, I bunt every single time,” Carpenter said. “I will always go for that hit. I’ve even tried it this year with two strikes; it didn’t work out well. But I’m not opposed to laying down the bunt in that situation.”

Because there was no third baseman to retrieve the ball, that fell on Hernandez to recover and prevent Carpenter from going to second.

“I'm a righty,” Hernandez said. “So, when I released the ball, I fell to the left side. I tried just to grab it. He's a veteran guy. He bunted it very well.”

Hernandez still executed his pitches and induced Paul DeJong to lift a fly ball to short center field.

But center fielder JT Riddle, a natural shortstop who is being used in center to increase his versatility, and second baseman Starlin Castro had a miscommunication and the ball dropped. Castro was charged with the two-base error that allowed Carpenter to score.

“To me, that's the center fielder's ball,” Mattingly said. “He's got to come get it. He's got to be aggressive. Star's going to keep going until he hears something. I'm not sure if he heard anything or not. It didn't sound like he did. But, for me, it's the center fielder's ball. He's got to come get it.”

Riddle was making his ninth MLB start in center field.

“I've played plenty of infield and went back on a fly ball,” Riddle said. “Take charge. I know when I'm going back as an infielder, I want to be able to hear the outfielder going back. I just need to be a little more vocal and say it louder next time.”

Added Mattingly: “That's part of our inexperience in the outfield.”

Miles Mikolas scattered six hits with four strikeouts in six shutout innings. Dexter Fowler broke the game open with a three-run homer off Austin Brice in the eighth inning.

Garrett Cooper extended his hit streak to 10 games with a single in the eighth, and he’s reached safely in 16 straight. But the Marlins have been shut out 13 times this season, and three times in their last nine games.

For Miami, though, Monday was a test to see how Hernandez would respond the second time around against the Cardinals.

In his last outing, a 7-1 Marlins loss on June 11 in Miami, Hernandez worked 5 2/3 innings, being charged with three runs. He fanned seven and walked one.

Often, when seeing a team twice in consecutive starts, the advantage goes to the hitters. That wasn’t necessarily the case for Hernandez, who pounded the zone. Of his career-high 101 pitches, 78 were strikes.

Hernandez is filling the rotation void created when left-hander Caleb Smith went on the injured list on June 7 due to left hip inflammation. Smith resumed his throwing program on Sunday and on Tuesday is scheduled to throw a bullpen session. There is no estimated time table for his return, but it could be at least another full week.

“He's been doing well,” Riddle said of Hernandez. “He looked really good. I got to play behind him in New Orleans. He looked really good. He had a good outing tonight. We just didn't get him any runs to support him tonight.”