Santos was the first of the Astros' four selections. They picked another right-handed pitcher, Tyler Brown, in the third round. Houston selected outfielder Zach Daniels in the fourth round and Shay Whitcomb was the final pick in the fifth round.
Santos was drafted out of Mount Saint Michael Academy in the Bronx, New York.
While his high school senior season was canceled in 2020, he did play on the international circuit last summer, earning a spot on the 2019 USA Baseball’s 40-man 18U National Team Trials Roster.
Santos was ranked as the 15th overall high school prospect by Baseball America and as the 56th overall player in the draft by MLB Pipeline.
"We were excited that Alex Santos was available to us at our 72nd pick," Director of Player Evaluation Charles Cook told reporters via conference call. "We have a good deal of history with him. We scouted him heavily last summer and then saw him in the early spring this year. We were attracted to him for a number of different reasons.
"He's a projectable young high school arm with a live arm, plus fastball that reaches the mid-90s. The breaking ball is his best pitch, a power slider with a workable changeup as well. We were really excited to see he was available to us."
Brown, 21, pitched in seven games for Vanderbilt during his junior year before the 2020 NCAA season was canceled. He posted a 1-2 record with one save, a 2.53 ERA (3ER/10.2IP), four walks and 14 strikeouts.
Brown was ranked as a top-100 prospect in the 2020 MLB Draft class by Baseball America, and was a 2020 first team preseason All-American selection by both D1Baseball and Perfect Game.
During his 2019 sophomore season, Brown set a Vanderbilt single-season record with 17 saves, which also led the Southeastern Conference and ranked second in the nation. Brown’s 21 career saves at Vanderbilt are the second-most all-time in the school’s history.
When asked if they believed Brown could be a starter, Astros scouting director Kris Gross said "absolutely."
"He's got four pitches to work with, a touch of 97, pretty low effort delivery," Gross said. "I think the kid believes he's a starter as well."
Daniels, 21, appeared in 17 games in what was his junior year at Tennessee this season.
In those games, he had a .357 batting average with four home runs and 18 RBI. Daniels was named the 2020 Round Rock Classic MVP after batting .333 (4 for 12) with one home run and three RBI.
D1Baseball had Daniels rated as the 48th overall MLB Draft prospect.
Daniels is considered a bit of a project -- a center fielder with raw power, who can run.
Astros executives acknowledge Daniels had been inconsistent early in his college career, but he started to show improvement before sports shut down.
Whitcomb, 21, batted .333 (27 for 81) with four doubles, five homers, 15 RBI and a 1.008 OPS (.440 OBP/.568 SLG) in 20 games for the University of California San Diego, a Division II school, during the shortened 2020 season.
Whitcomb was named to the 2020 California Collegiate Athletic Association (CCAA) All-Star Team, was named the 2019 CCAA Most Valuable Player, and was tabbed the 2018 CCAA Freshman of the Year.