ST. PETERSBURG -- As soon as Orioles first baseman Derrek Lee closed his glove on the final out of the 4-1 Opening Day win over the Rays, top pitching prospect Zach Britton's phone went off: he was getting the call to join Baltimore.

"I expected to be in [Triple-A] Norfolk for the next 20 days," said Britton, who was still in a state of shock over Friday night's events, which included placing starter Brian Matusz on the 15-day disabled list with a strained intercostal muscle. "I expected to be the last guy coming up."

But with Matusz sidelined anywhere from three to six weeks and the instability in the O's rotation with Justin Duchscherer on the DL (left hip soreness), Brad Bergesen (right forearm strain) still getting back his arm strength and Chris Tillman posting an uneven spring, the Orioles no longer have the luxury of keeping the 23-year-old Britton from accruing service time.

"Sometimes fates just don't allow it and you've got to do what you've got to do," president of baseball operations Andy MacPhail said. "We thought we had five starters and Zach would be sixth and Justin seven. Unfortunately, we lost one before we threw a pitch. And we just have to adjust."

Britton, who pitched to a staff-leading 1.35 ERA this spring, is hardly a contingency plan. A power pitcher who can sink the ball and induce groundouts at an astounding rate, he was named the organization's Minor League Pitcher of the Year in 2010, and pitched to a 2.98 ERA in 12 games after being promoted to Triple-A. Britton would have broken camp if not for the Orioles early off days and the tradeoff of 20 days in the Minors for an extra year of team control.

"I think he's ready," catcher Matt Wieters said of Britton. "There is always going to be learning things he's going to go through the first couple of times through the league, but his stuff plays at this level just as well as anybody's."

Britton, who was still in Sarasota for Minor League camp, said he will draw confidence from his success in his first Major League Spring Training, including his last start against a Tigers lineup full of regulars.

"I have a lot of confidence for Sunday," said Britton, who admitted to being "nervous as hell" following his first Major League Spring Training game against the Phillies.

"Obviously, my adrenaline is going to be going," he added. "It's not going to be like [facing] Philly. Multiply that by 200 times and it'll be something like that. Not to make anybody worried about me out there. I just think it's stupid to think I'm not going to be nervous. But I have a lot of confidence that I can get the job done."

So does Matusz, who understandably had a mixed reaction to Friday's turn of events.

"I'm not happy about my situation, where I'm at, but Zach pitched his butt off and put himself in a situation that he's just one call away," Matusz said. "He got that call. We know Zach's ready. He showed it all spring. I'm excited for him. I'm excited for his opportunity and I can't wait to see how well he does at this level."

Britton will pack his things Saturday morning and expects to be at Tropicana Field before the Rays-Orioles game. He threw a bullpen on Thursday and watched Opening Day starter Jeremy Guthrie post eight scoreless innings against the Rays, unaware that his Major League debut was less than 48 hours away.

"I've got a lot to live up to," Britton said. "I'm really excited, and I'm going to do my best."