While the prospect of facing the defending World Series-champion Yankees is a daunting way to debut, the 24-year-old Arrieta, who arrived in Baltimore on Wednesday, feels up to the task.
His contract was purchased from Triple-A Norfolk on Thursday. Left-hander Alberto Castillo was designated for assignment.
"It's a lot bigger names in the box score, but it's the same game," Arrieta said in a phone interview with MLB.com. "Whether it's A-Rod or some hitter from Scranton, I have to approach [Thursday] like any other start."
The Yankees have won 10 straight games against Baltimore this season and Arrieta will get a chance to help the O's buck the trend. The organization likes Arrieta's confidence, and he will need every bit of it Thursday.
"We feel that he's one of the big guys that we'll be counting on in the future," interim manager Juan Samuel said. "Why not bring him [up]? I know we're going to throw him in the fire against these guys, but hey, we don't get to pick who we play or who we face. It's a challenge for him. We'll see how he reacts."
While the initial belief was that Arrieta would come up from Triple-A Norfolk on Saturday to take the place of Brad Bergesen -- who was moved to the bullpen for an unspecified amount of time -- Samuel said the O's felt it was more important to give Jeremy Guthrie an extra day of rest and keep Arrieta on schedule.
The decision -- which was thought to be nearly inevitable -- was unexpected for Arrieta, given the sudden timing.
"I thought maybe I'd come up for Saturday," he said. "I really didn't think it was going to happen like this.
"I was shocked, very excited. There were just a lot of emotions that came over me."
The news was delivered by Norfolk pitching coach Mike Griffin following Tuesday's Tides game, and came with a word of warning: Be yourself, or else.
"He's real confident and I'm really confident that what I've been doing will up work up there," Arrieta said. "If I try to change things, that's where I get in trouble."
Griffin half-joked that if he saw Arrieta getting away from what has made him so dominant at Triple-A, the pitching coach would drive up to Baltimore and "basically kick my butt," Arrieta said.
Given Arrieta's numbers -- which include a 1.85 ERA in 12 games -- he'd be wise to listen to Griffin. In his past three Triple-A starts, Arrieta has allowed just two runs and 16 hits while striking out 23 over 22 innings. He is 6-2 on the season and has held opponents to a .195 batting average.
The Orioles' fifth-round Draft pick in 2007, Arrieta pitches off of a fastball that touches the high 90s, and he will look to attack the strike zone early and often against a notoriously patient Yankees lineup. While control has been an issue at times, Arrieta said he is throwing his best baseball as of late.
"Everything kind of clicked on all cylinders at the right time," he said.
"I've been pitching deep into games. I feel like I've been doing everything the team needs to help win."
Guthrie will open the Orioles' Interleague series Friday against the Mets, a start he was told about Sunday morning. Other than a slight tweak in his bullpen schedule, Guthrie hasn't done anything different and said physically he feels fine.
"Nothing's wrong. Nothing's been wrong," Guthrie said. "Obviously the proof is in the pudding. If you throw in the bullpen, you play catch every day and you pitch every five days, then you're doing what every other pitcher is doing, which is preparing yourself, whatever it takes in between, and go out there and pitch."
"I learned a long time ago not to try to plan out when I pitch," he said. "I tried that for a couple years and it didn't work out too well, so now i just say 'Yes sir, thank you.'"
Brittany Ghiroli is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.