The selection was on the heels of the Red Sox taking high school infielder Michael Chavis with their first-round selection (26th overall).
"We take the best player on the board," said director of amateur scouting Amiel Sawdaye. "If the two best players are a high school pitcher and a high school middle infielder, then that's who we're going to take. We're not looking to diversify or draft for need. It so happened those were the next two players. Those were players we're very excited about, have a lot of conviction on, scouted for a long time, had a lot of history with. That's kind of how it shook out."
Kopech is a lanky righty (6-foot-4, 195 pounds) out of Mt. Pleasant High School (Texas).
"As far as the mechanics, those of you guys that have seen it, he's got an electric arm," said Sawdaye. "We really like the way he commands his fastball. The delivery kind of reminds a little -- it's got a little Jered Weaver in it."
Kopech's fastball has been clocked mainly in the low 90s, with plenty of room for an increase as he fills into his body.
"We've been scouting this guy for about two years. I think people that saw him in the Under Armour game could see how he commanded his fastball and commanded his secondary pitches," said Sawdaye. "Obviously we're really excited to get him out and watch him develop."
There is also a lot of upside to Kopech's breaking ball, which led to him striking out Alex Jackson, the sixth player taken on Thursday by the Mariners, in a showcase game at Wrigley Field.
In a tweet last night, Kopech tweeted out a picture in which he was embracing his dad after getting selected, and provided the caption, "Greatest moment of my life."
Kopech has a commitment to the University of Arizona.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.