Butler, the Rockies' No. 2 prospect takes the spot vacated when Franklin Morales was moved to the bullpen, giving the Rockies one of their most anticipated arrivals in years.
His contract will be picked up Friday, and a move likely to correspond with Butler's callup was made Thursday when the Rockies put left-handed reliever Boone Logan on the disabled list with left-elbow inflammation. Logan has been pitching through the ailment for some time, and the Rockies are hopeful he'll be back with the club without a prolonged DL stint.
Butler has gone 4-4 with a 2.49 ERA at Tulsa this season. In a three-start stretch in May, he went 3-1 with a 0.67 ERA, pitching at least seven innings in each game.
"Mentally he's been preparing himself for this," manager Walt Weiss said before Thursday's series finale with the D-backs. "Some guys get ambushed when they get called up to the big leagues. I think he's prepared himself mentally for this for several months. He's probably already pitched his Major League debut in his mind."
In his first big league Spring Training camp, Butler impressed his coaches teammates with his confidence and composure. As he prepares to face a powerhouse Dodgers lineup, he's taking the assignment in stride.
"It's another team," Butler said. "It's another guy in the box. I'm going to attack them and give the guys a chance to win. They're going to play some defense behind me and score some runs."
Weiss recalled his own Major League debut with a measure of embarrassment. He entered the game as a pinch-runner for Mark McGwire and was promptly thrown out stealing second. Nevertheless, what lingers is the feeling of "floating off the ground" as he took the field.
Knowing Butler will have some of those same feelings, the manager is nevertheless confident the promising pitcher from Chesapeake, Va., and Radford University is equipped to handle the task in front of him.
"He's got a great arm," Weiss said. "He's a great competitor. He seems unflappable. I think he'll take the mound on Friday night and expect to do well. That's more than half the battle."
His power arm is his calling card, and Butler compliments it with a curve, changeup, and slider.
Butler bonded with Rex Brothers and LaTroy Hawkins during Spring Training, and the familiar faces in the Rockies clubhouse have helped him feel at home in a new setting.
"I'll just try to be even keeled," he said of the big league challenge. "The roller-coaster is not a good thing. Just go out there every day, try to keep the same mentality -- attacking guys. Give the team a chance to win."
Butler will wear No. 31, the number of one of his heroes from childhood, Greg Maddux.
"I was a Braves fan which isn't good because they're lining up for my second start," Butler said. "I was a big [John] Smoltz and Maddux fan. I liked the different ways they pitched, obviously Smoltz being a little more of a power guy and Maddux being a finesse guy, moving the ball around."
Despite his own power right arm, he's focused on adding some finesse, and adopting a game plan well-suited to Coors Field.
"I've been trying to get contact early, get some ground balls to give the guys a chance to make some plays behind me," Butler explained of his approach in Tulsa. "When I first got to college, I'd go five innings with seven or eight strikeouts but that wasn't beneficial to the team. I was wearing down the bullpen and not giving us a chance to win."
Butler's debut will come on Day 2 of the 2014 First-Year Player Draft, two years and two days after he was taken by the Rockies in the first round. In 2013, his first full season as a pro, he moved from Class A Asheville, to Class A Advanced Modesto and ultimately to Double-A Tulsa, posting a combined 9-5 record and a 1.80 ERA -- the lowest in the organization.
"It's crazy to think how quick it happened," Butler said. "I've made substantial strides since rookie ball to where I am today. And there's still things that I haven't even learned about that are going to be beneficial in the future for me."
While keeping expectations in check, Weiss is eager to see Butler contribute to the club.
"He's been very dominant at times over the last couple of seasons," Weiss said. "We knew he was a big leaguer, it was just a matter of when. And the time is now."