MIAMI -- In a season where they are going through plenty of growing pains, rotation stability has been the backbone for the Marlins. For the most part, the starters have done their part, showing plenty of promise, and until now, continuity.

On Tuesday, in their 65th game, the Marlins finally needed a sixth starter. Elieser Hernandez got the nod in place of left-hander Caleb Smith (left hip inflammation), and the 23-year-old kept his team in the game for 5 2/3 innings.

But the Cardinals capitalized on an error and three straight walks in the sixth inning, and blew the game open late against the Marlins in their 7-1 win at Marlins Park.

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The Marlins have dropped six straight, and look to avoid a three-game sweep on Wednesday.

During the rough stretch, Miami’s pitching depth is being tested. Smith, who has arguably been the Marlins’ best starter, felt discomfort in his hip after his fastball velocity dropped by two mph in a Thursday loss at Milwaukee. He went on the injured list the next day, and Hernandez was officially added to the roster on Tuesday, getting recalled from Triple-A New Orleans.

“Really good,” Marlins manager Don Mattingly said of Hernandez. “Aggressive. Throwing strikes. Using his pitches. Elevating his fastball. Throwing some fastballs down. Using his changeup. His slider is getting better. A little bit more consistent with that. And he pitched well.”

Hernandez showed poise and worked a career-high 5 2/3 innings, allowing three runs on five hits with seven strikeouts. Of his 96 pitches, he induced 18 swinging strikes.

“I felt really good,” said Hernandez, a Venezuelan native, through an interpreter. “I was trying go out there, have fun, and mostly, help the team.”

But Hernandez ran out of steam in the sixth inning, and didn’t receive much help. Shortstop Miguel Rojas, trying to turn an inning-ending double play after snaring Yadier Molina’s line drive, bounced a throw to first base trying to double-up Marcell Ozuna. When the ball skipped past Garrett Cooper, Paul Goldschmidt, who doubled, scored the go-ahead run from third, making it 2-1.

“I feel fearless,” Rojas said. “I always play to win. I don't play to make errors or avoid errors. I feel like that is part of the game. If I make that play, you guys probably shouldn't be here talking to me about it.”

Hernandez, making his first big league start since last Aug. 23 against the Braves, was lifted for Jarlin Garcia, who walked the only batter he faced. Jeff Brigham then issued back-to-back walks, including to Harrison Bader, forcing in the third run.

The Cardinals broke the game open after that, scoring four runs in two innings off Adam Conley, whose role is shifting more to a long-relief position after being in setup situations.

Miami’s offense managed one run, on Rojas’ RBI single in the fourth, off Dakota Hudson. That was all the support Hernandez had when he was in the game.

The Marlins have dropped the first five games on their homestand after they went 4-2 on the road at San Diego and Milwaukee.

“I feel like we went away from our plan, offensively,” Rojas said. “That's the only way I can see it. We got back home, coming from a couple of good ballparks to hit. It looks like we were a different team. We've been having a problem with sinkerballers.”

Making the most of his opportunity, Hernandez did his part, and showed the importance of starting pitching depth. At New Orleans, he impressed with a 3-1 record and 1.13 ERA in nine starts. He fanned 69 in 48 innings.

“He does a lot of things well,” Mattingly said. “He holds runners. He does a lot of things really well. We'll see where it goes.”

The Marlins have yet to commit to Hernandez to stay in line in the rotation, because they remain hopeful Smith won’t be out too long.

“Smitty, we'll make sure that he's medically fine before we get him back out there,” Mattingly said. “We feel like it's going to be short. We'll make sure he will do all the steps before he goes back out there.”

The rotation took another blow with Opening Day starter Jose Urena scheduled to go on the injured list with lower back tightness. Urena had been set to face the Cardinals on Wednesday in the series finale. But right-hander Jordan Yamamoto will be recalled from Double-A Jacksonville to make his MLB debut.

A Rule 5 Draft claim from the Astros in 2018, Hernandez’s path to the big leagues was pretty much backwards. He found himself making the jump from Class A Advanced to the Majors, instead of having the opportunity to develop in the Minor Leagues. Because he did so, he is now eligible to be optioned to the Minors or stick with Miami, either as a starter or long reliever.

“I think what he's been doing in Triple-A is pretty impressive,” Rojas said. “The PCL is a hitter's league, and he's been able to shut that league down, and pitch pretty well. He threw the ball really well tonight, kept them off balance and gave us an opportunity to win.”