Holding him back, however, was command.
What manager Mike Matheny described as "overthrowing" and "jumpy," Reyes explained away as trouble getting his mechanics in sync. What it led to were four walks and extended innings. By the time Matheny pulled Reyes with two on and two out in the fifth, the rookie's pitch count sat at 89.
"I was a little out of rhythm with my mechanics, so I wasn't able to establish the ball down early in the game," Reyes said. "It was a big day being out there as a starter, but unfortunately, I wasn't able to execute pitches consistently."
It's the same issue that hampered Reyes, the organization's top prospect, throughout much of his Triple-A season. In 14 starts with Memphis, Reyes posted a walk rate of 4.4 and averaged 19 pitches per inning. Those efficiency concerns were a contributing factor in the Cardinals' decision to start him as a big league reliever.
The need to thrust him into a starting spot came after Leake was diagnosed with shingles.
But while there is clear area for growth, there's also evidence of great promise. Though an inherited runner he left to Zach Duke scored in the fifth, Reyes opened his Major League career with 14 scoreless innings. It was the third longest scoreless streak by a rookie starting his Cardinals career.
"He had an impressive run of being able to make some tough-count pitches and really using his secondary stuff to get him out of trouble," Matheny said. "It's not something that you normally see from a kid's first start."
Reyes' repertoire has been as dynamic as advertised, too. While the triple-digit fastball generates much of the excitement, Reyes has showcased an above-average curveball and changeup that have complemented his four- and two-seam fastballs. Reyes threw 22 changeups, ranging in velocity from 89-to-93 mph and generated six swing and misses on the pitch.
Matheny later described the pitch as "incredible."
"I think it's better than what he even realizes," Matheny added, "and Yadi [Molina] sees that, too."
The Cardinals have not committed to what's next for Reyes, aside from he'll have a place on the Major League roster. If Leake remains sidelined, Reyes would be an option to draw another start. If he's not needed in the rotation, he'll resume his role in relief.
Regardless, he's positioned to play an important role for the club down the stretch.
"Amazing arm, very poised, very polished," Duke said of the rookie righty. "He's got a great career ahead of him."