WEST PALM BEACH, Fla. -- Marlins top prospect Sixto Sánchez flashed triple-digit velocity during his scoreless Grapefruit League debut in Miami's 6-5 win over the Astros on Monday afternoon at The Ballpark of the Palm Beaches. He permitted two hits, walked one and didn’t record a strikeout on 31 pitches (21 strikes) across 1 2/3 innings.

In a 10-pitch first, Jose Altuve ambushed the first offering from MLB Pipeline's No. 15 overall prospect for a single up the middle. Two pitches later, Sánchez induced a ground-ball double play. Facing Carlos Correa, he reached 100 mph twice and broke Correa's bat before the matchup ended on an inning-ending groundout to first.

In Sanchez's 21-pitch second, Kyle Tucker led off with a single to center on a 99-mph fastball to culminate an 11-pitch at-bat, which included six straight foul balls with the count at 1-2. After falling behind 3-0 to the next batter, Yuli Gurriel, Sánchez got it back to 3-2 but issued ball four. With two runners on, pitching coach Mel Stottlemyre Jr. came out of the dugout for a mound meeting to tell the flamethrower he didn't want to push him too much. Sánchez's outing ended when the next batter, Aledmys Díaz, grounded into a 5-3 double play. Manager Don Mattingly called on reliever James Hoyt for the final out.

"I felt very well for my first Spring Training game in 2021," Sánchez said via an interpreter during a Zoom call. "I was just going out there with the same plan as always. First inning, I was missing my spot a few times, and same thing happened again in the second."

The 22-year-old right-hander, wearing No. 45 on the big league mound for the first time in honor of his hero, Pedro Martinez, had never appeared in a Spring Training game until Monday. In his previous two springs with the organization, Sánchez had been eased into a throwing program.

This spring, Sánchez initially was delayed getting to camp from the Dominican Republic because of visa issues, then had a false positive COVID-19 test that set him back a couple of days as he waited for results. On March 6, he returned to camp before throwing a bullpen session the following day and a 26-pitch live batting practice last Thursday.

"I don't feel frustrated, to be honest, but it was a weird feeling," Sánchez said. "I was getting ready. I was getting that momentum, and I was also getting ready for a live BP exactly that week. And then that false positive came out, and it kind of ruined that momentum."

Barring a setback, Sánchez will follow the same five-day progression as his rotation counterparts, putting him in line to pitch again at 6:05 p.m. ET on Saturday against the Nationals in West Palm Beach. The plan would call for him to add an inning and/or 15-20 pitches.

"With Sixto, it's a matter of letting him kind of dictate his plan to ascend to a point where, as long as he's feeling good, it keeps progressing," Mattingly said during a Zoom call Monday morning. "If we have to slow down and give him an extra day's rest, then we'll do that. And he's been a guy that in the Minor Leagues has always gotten that extra day's rest. And so we're basically transitioning him to every five. And that's where we're going to be careful. If in between he feels like he needs an extra day, then we'll do that."

Opening Day is scheduled for April 1, which gives Sánchez less than three weeks to build up his pitches. Miami also has two off-days (April 4 and 9) within the first nine dates of the season, so the club could go with four starters. Rotation mates Sandy Alcantara, Pablo López and Elieser Hernandez have made three spring starts, while Trevor Rogers is slated for his third on Tuesday. Despite that, Sánchez doesn't feel too far behind.

Last week, Stottlemyre noted Sánchez will have an innings cap this season, though the Marlins have a plan for how he can appear in September games. Upon his callup in 2020, Sánchez made seven regular-season starts, then another two in the postseason, for a combined 47 frames. He dazzled with ace potential, recording four strikeouts on 100-plus-mph pitches (most by any Marlins starting pitcher in the pitch-tracking era) and a dynamic fastball/changeup combination. According to Baseball Savant, his two-seamer (17.3 inches) and changeup (17.1 inches) have near identical movement. Sánchez was in the 98th percentile for fastball velocity and 86th percentile for xERA and xwOBA. All this without ever having pitched above Double-A, with just 18 starts at that level in 2019.

Through his first five MLB starts, Sánchez boasted a 1.69 ERA. But he faltered over his final two outings when facing ballclubs for the second time (11.57 ERA).

As part of Sánchez's development, Stottlemyre would like the rookie to use his changeup more. According to Baseball Savant, Sánchez turned to it 26.7 percent of the time -- most of his five-pitch arsenal. Then came the sinker (24 percent) and four-seamer (23.8 percent). Sánchez called the changeup the pitch he can control the most besides his fastball, and one he utilizes to get out of jams. Seeing Altuve jump his first-pitch fastball reminded him that batters know he throws hard and will be waiting for the heat. He will have to find other ways to get them out.

"I think we all saw a glimpse last year of what this guy's capable of doing," Stottlemyre said during a Zoom call last week. "He's 22 years old, he's still got a lot to learn. It's easy when you see him out there to forget that side. So he still has to learn about the league, knowing where his adjustments are and taking some bumps and some bruises and seeing how he reacts to those situations. We all think he needs to throw more changeups. ... It's easy to get enamored at somebody that throws 97-100 [mph] to want to lean on that fastball, but in reality, he's got one of the best changeups in baseball. Making sure he uses that enough.

"And you know the evolvement, the willingness to get his other pitches in the zone -- the slider and the breaking ball -- and figuring out when to use those pitches, and to who you use them to, so he's got a lot to learn. I look at where Sandy was two years ago and where [López] was -- this guy does some things already that maybe those other two guys didn't do. This guy's a strike thrower, so he's just got to figure out the league. When they start game planning, where his adjustments are going to be. And he'll have to go through all that. Trying to keep him healthy and on the field."