Guthrie will be followed by Brian Matusz in the opening series against the Tampa Bay Rays, with right-hander Jake Arrieta tentatively scheduled to pitch the April 4 home opener vs. the Detroit Tigers.
"It's a big opportunity and a big honor," said Guthrie, who found out about the assignment a few weeks ago.
This will be Guthrie's third Opening Day start for the Orioles in the last four seasons. He is coming off an impressive 2010 campaign, in which he made 32 starts and hit the 200-inning mark for the second straight year.
"That's my ultimate goal," Guthrie said. "I don't set a number on wins or any other stat. But I do want to make all my starts. I want to get as deep as I can into the games, and that comes from being aggressive and throwing strikes. Those will be my only two goals this season."
The 31-year-old Guthrie went 8-4 with a 2.76 ERA in 14 second-half starts, and is expected to anchor an O's rotation that will feature three members who are 25 and under. Guthrie went 11-14 with a cumulative 3.83 ERA in 2010, and is 38-48 with a 4.15 ERA in 143 games (122 starts) for his career.
The final game of the Rays series is the team's only question mark, although it's believed Brad Bergesen has the edge over the 22-year-old Chris Tillman. Top pitching prospect Zach Britton is expected to start the season with Triple-A Norfolk, and remain there until at least April 21. That will buy the team an extra year of control over the talented lefty.
Showalter said the team is still mulling whether to take an extra reliever or position player with the four-man staff.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.